Application Report
SLAA514 – December 2011
USB Keyboard Using MSP430™ Microcontrollers
David Racine, Luis Reynoso ............................................................................................ MSP430 Apps
ABSTRACT
This application report describes a low-cost highly-flexible composite USB keyboard implementation based
on MSP430F5xx/MSP430F6xx families. Schematics and software are included allowing for an easy
implementation and customization.
The document explains basic necessary concepts but familiarity with the MSP430™ USB Developers
Package (MSP430USBDEVPACK) and USB HID specification is assumed.
Source code and additional information described in this application report can be downloaded from
http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/USBKBD_430/latest/index_FDS.html.
1
2
3
4
5
6
7
Contents
Introduction .................................................................................................................. 2
Implementation .............................................................................................................. 2
Software ...................................................................................................................... 6
Hardware and Peripheral Usage ........................................................................................ 12
Using the USB Keyboard ................................................................................................. 12
Schematics ................................................................................................................. 15
References ................................................................................................................. 16
List of Figures
1
Key Matrix .................................................................................................................... 3
2
Keyboard Schematic........................................................................................................ 3
3
Detection of a Key Using Column-Interrupt Method .................................................................... 4
4
Detection of a Key Using Polling Method ................................................................................ 4
5
"Ghost" Key Detection ...................................................................................................... 5
6
USB Keyboard Software Modules ........................................................................................ 6
7
USB Keyboard Flow Diagram ............................................................................................. 7
8
Digital Keyscan Flow Diagram ............................................................................................ 9
9
USB Keyboard in Windows Device Manager .......................................................................... 13
10
Testing the HID Custom Interface ....................................................................................... 14
11
Schematics ................................................................................................................. 15
List of Tables
1
VID/PID Used by the Device .............................................................................................. 5
2
HID Keyboard Report Format ............................................................................................. 8
3
Communication Protocol Report Descriptor ............................................................................. 8
4
Implemented Protocol ...................................................................................................... 8
5
Configuration Constant Table ............................................................................................ 11
6
ScanCodes ................................................................................................................. 11
7
MSP430F550x/5510 Peripheral Usage ................................................................................. 12
8
MSP430F550x/5510 Pinout Usage ..................................................................................... 12
MSP430, Code Composer Studio are trademarks of Texas Instruments.
IAR Embedded Workbench is a trademark of IAR Systems.
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USB Keyboard Using MSP430™ Microcontrollers
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1
Introduction
1
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Introduction
This application report describes the implementation of a USB keyboard with the following characteristics:
• 101 keys, 2 LEDs: standard HID keyboard and LED usage
• 16x8 matrix: allows for easy customization of different keyboard layouts
• Composite USB device: In addition to the keyboard interface, it includes an HID-datapipe back-channel
which can be used to transmit any custom data
• HID boot protocol support, allowing keyboard to be used to interface with a PC's BIOS
• "Ghost" key handling in software, to prevent errors from multiple key presses
• Uses MSP430F550x/5510 low-cost USB family
The Texas Instruments MSP430F550x/5510 devices are ultra-low power microcontrollers featuring a
powerful 16-bit RISC CPU, 16-bit registers, and constant generators that contribute to maximum code
efficiency. In addition, this MSP430 family includes an integrated USB and PHY supporting USB 2.0 fullspeed communication, four 16-bit timers, a high-performance 10-bit analog-to-digital converter (ADC), two
universal serial communication interfaces (USCI), hardware multiplier, DMA, real-time clock module with
alarm capabilities, and 31 or 47 I/O pins.
2
Implementation
2.1
Key Matrix
The USB keyboard presented in this application report implements a key matrix of rows and columns
similar to smaller keypads like the one shown in the application report Implementing An Ultralow-Power
Keypad Interface with MSP430 (SLAA139).
This implementation uses a 16 rows x 8 columns matrix, which allows up to 128 keys, but it actually uses
only 101 keys in total.
The key matrix is shown in Figure 1.
2
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Implementation
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Row0
P2.0
Col0
P1.0
Col1
P1.1
Col2
P1.2
Col3
P1.3
Col4
P1.4
Col5
P1.5
Col6
P1.6
Col7
P1.7
Keypad
Enter
Keypad
-
Keypad
+
Keypad
2
Keypad
3
Keypad
.
Keypad
1
Keypad
/
Keypad
9
Win
Keypad
7
Home
PageUp
Keypad
NumLock
Tab
~
`
1
Q
A
Row1
P2.1
Row2
P2.2
Keypad
0
Row3
P2.3
Right
Alt
Left
Alt
Row4
P2.4
C
Space bar
F3
F4
CapsLock
3
E
D
Row5
P2.5
X
Z
F2
F1
Esc
2
W
S
Row6
P2.6
V
B
G
T
5
4
R
F
Row7
P2.7
M
N
H
Y
6
7
U
J
Row8
P3.0
>
.
ê
|
\
F11
F10
9
O
L
Row9
P3.1
Right
Shift
Left
Shift
Row10
P3.2
<
,
Keypad
*
F7
F6
F5
8
I
K
Keypad
8
F9
Row11
P3.3
ç
Row12
P3.4
Right
Ctrl
Left
Ctrl
Row13
P5.0
?
/
é
_
-
F12
0
P
{
[
:
;
Row14
P5.1
“
‘
Enter
PrtScr
End
+
=
Back
space
}
]
Page
Down
è
F8
Pause
Scroll
Lock
Keypad
4
Keypad
5
Keypad
6
Row15
P2.0
Figure 1. Key Matrix
...
Coln
Col1
Col0
Each key works like a switch, and pulldowns are implemented on each column, keeping the idle state low
(see Figure 2).
Row0
Row1
...
Rown-1
Rown
Figure 2. Keyboard Schematic
There are multiple ways to scan a key matrix, but this application report uses two methods, referred in this
application report as: column-interrupt and polling.
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Implementation
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In the column-interrupt approach, all rows are actively driven at the same time and columns are configured
to interrupt the processor when any single key is pressed.
This method is useful in low-power modes, because any key can wake up the microcontroller; however, it
is important to remark that the key press is only used for that purpose, because it does not provide the
exact key being pressed.
Figure 3 shows the key matrix behavior when the Enter key is pressed in column-interrupt mode. Actively
driven rows and columns are shown in red. Notice that the Col1 pin would detect a change when the Enter
key is pressed, but the effect would be the same for any other pin pressed in the same column.
Row0
P2.0
Col0
P1.0
Col1
P1.1
Col2
P1.2
Keypad
Enter
Keypad
-
Keypad
+
Row1
P2.1
.
.
.
Row14
P5.1
...
Keypad
9
“
‘
Row15
P2.0
Enter
PrtScr
è
F8
Figure 3. Detection of a Key Using Column-Interrupt Method
After the system is awake due to a key press using the column-interrupt approach, the polling method can
be used to determine which key(s) is(are) being pressed (see Figure 4). In the polling method, each row is
scanned separately driving one row at a time in sequential order. The columns are then read giving the
exact keys being pressed.
Row0
P2.0
Col0
P1.0
Col1
P1.1
Col2
P1.2
Keypad
Enter
Keypad
-
Keypad
+
Row1
P2.1
.
.
.
Row14
P5.1
Row15
P2.0
...
Keypad
9
“
‘
Enter
PrtScr
è
F8
Figure 4. Detection of a Key Using Polling Method
One of the caveats when using this method is that particular patterns can cause unwanted connections,
known as "ghost" keys. This behavior is caused when three or more keys sharing rows and columns are
pressed at the same time (see Figure 5).
4
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Row0
P2.0
Col0
P1.0
Col1
P1.1
Col2
P1.2
Keypad
Enter
Keypad
-
Keypad
+
Row0
P2.0
Keypad
9
Row1
P2.1
Row1
P2.1
.
.
.
Row14
P5.1
“
‘
Row15
P2.0
Enter
PrtScr
è
F8
...
.
.
.
Row14
P5.1
Row15
P2.0
1. Enter, PtrScr and è
keys are pressed
Col0
P1.0
Col1
P1.1
Col2
P1.2
Keypad
Enter
Keypad
-
Keypad
+
Row0
P2.0
Keypad
9
Row1
P2.1
“
‘
Enter
PrtScr
è
F8
...
.
.
.
Row14
P5.1
Row15
P2.0
Col0
P1.0
Col1
P1.1
Col2
P1.2
Keypad
Enter
Keypad
-
Keypad
+
...
Keypad
9
“
‘
Enter
PrtScr
è
F8
3. Driving Row15 detects è but
it incorrectly detects F8
2. Driving Row14 detects Enter
and PtrScr
Figure 5. "Ghost" Key Detection
The software included in this application report detects potential "ghost" keys and does not report them to
the host.
2.2
USB HID
This application report uses the MSP430 application programming interface (API) stack found in the
MSP430 USB Developers Package (MSP430USBDEVPACK).
The stack is configured to work as a composite HID-HID interface with the first interface being a standard
Keyboard and the second interface used as a DataPipe. One of the advantages of using this
implementation, which using only HID interfaces, is that no drivers are required.
Although the relevant code for the keyboard implementation uses the standard keyboard interface, the
DataPipe interface was added to provide users with more flexibility and to facilitate customization.
This interface can be used to send or receive any type of data to/from the host, so that the MSP430
microcontroller not only performs the job of a digital keyboard, but it can also be used to perform other
jobs taking advantage of the same USB interface and the rest of the peripherals. Some examples include
reading sensors using ADC and reporting to PC, controlling actuators using timer PWMs, etc.
It should be noted that while the host OS interprets and uses the data from the standard keyboard
interface without additional applications or drivers, in the case of the Datapipe interface, a host application
is required. Texas Instruments provides an HID API which enables communication between a PC and a
MSP430 microcontroller running the HID API stack. This HID API is available in executable format and
source code in the MSP430 USB Developers Package (MSP430USBDEVPACK).
The keyboard interface supports Boot protocol, which allows it to work with HID-limited hosts (such as
some BIOS).
VID and PID can be modified according to the particular application but the default code used for this
example uses the values shown in Table 1.
Table 1. VID/PID Used by the Device
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VID
0x2047
PID
0x0401
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Software
3
Software
3.1
Tools
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The software included in this application report was built and tested using:
• IAR Embedded Workbench™ for MSP430 5.30.4 IDE
• Code Composer Studio™ (CCS) 5.1.0 IDE
3.2
Software Implementation
Figure 6 shows the software layers for the USB keyboard.
Application
USB Keyboard
Comm
Protocol
Keyboard Report
USB HID
DKS (Digital Keyscan)
USB API
MSP430 Driverlib
UCS
PMM
ticktimer
Timer
GPIOs
DMA
USB
Hardware
Figure 6. USB Keyboard Software Modules
Software is designed in a modular way, re-using existing TI libraries such as driverlib and the USB API
and adding new modules from low-level drivers to application level. These modules include:
• USB Keyboard
Description
Main application initializing the microcontroller, peripherals, and executing a loop checking and
servicing the rest of the modules.
Files
Src\TI_USBKBD_main.c
Flow Diagram
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Initialize:
PMM,
UCS (clocks),
GPIOs,
Timers,
USB,
Timer,
USB Keyboard
Initialization
USB Active?
Y
USB
Suspended?
N
Disable DKS
Y
Sleep
Y
Process RX data
from HID0/HID1
N
Data
received?
N
Initialize DKS and
KBD_Report
modules
Y
First loop?
N
USB or
Keyboard
activity?
N
Y
Wake MCU
Attend DKS
module
Attend
KBD_Report
module
Y
Force Remote
Wakeup
Pending
tasks?
N
Sleep
N
USB, Timer or
Keyboard activity?
Y
Figure 7. USB Keyboard Flow Diagram
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Software
•
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Keyboard Report
Description
Handles the HID Keyboard report, adding and removing keys from the report depending on
press/release events and sends the report to the USB Host.
Files
Src\TI_USBKBD_HIDKBD_report.c
Src\Include\ TI_USBKBD_HIDKBD_report_public.h
HID Keyboard Report Format
Table 2. HID Keyboard Report Format
Byte0
•
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
Right GUI
Right Alt
Right Shift
Right Ctrl
Left GUI
Left Alt
Left Shift
Left Ctrl
Byte1
Reserved
Byte2
Key_array[0]
Byte3
Key_array[1]
Byte4
Key_array[2]
Byte5
Key_array[3]
Byte6
Key_array[4]
Byte7
Key_array[5]
Communication Protocol
Description
Handles the HID custom interface, which is used to transfer data to/from an USB host. The current
implementation shows a template that can be used for custom development.
This module uses the HID-Datapipe as defined in the USB API included in MSP430 USB Developers
Package (MSP430USBDEVPACK).
Files
Src\TI_USBKBD_comm_protocol.c
Src\Include\ TI_USBKBD_comm_protocol_public.h
HID Custom Interface Report Descriptor
Table 3. Communication Protocol Report Descriptor
Field
Size
Description
1 byte
The report ID of the chosen report (automatically assigned to 0x3F by
the HID-Datapipe calls)
Size
1 byte
The number of valid bytes in the data field
Data
62 bytes
IN Report
Report ID
Data payload
OUT Report
1 byte
The report ID of the chosen report (must be assigned to 0x3F by the
host)
Size
1 byte
The number of valid bytes in the data field
Data
62 bytes
Report ID
Data payload
Data Payload Protocol
Table 4. Implemented Protocol
8
Field
Size
CMD
1 byte
Data
61 bytes
Description
1 = Toggle CAPS LED
2 = Toggle NUM LED
Unused
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•
DKS (Digital KeyScan)
Description
Handles the digital keyboard scanning, detecting key press/release events, and reporting them to the
keyboard report module.
Files
Src\TI_USBKBD_DKS.c
Src\Include\TI_USBKBD_DKS_public.h
Flow Diagram
DKS is initialized in
“interrupt-column” mode by
default if no key is pressed.
Digital KeyScan
Interrupt-column
polling
Mode?
N
Key press
detected?
Scan key matrix
Y
Change to Polling
mode
Release
None
Inactive timer N
expired?
Key event?
Y
Press
Remove key from
report
Change to
Interrupt-Column
mode
Y
“Ghost” key?
N
N
Key
debounced?
Increment
debounce counter
Y
Add key to report
Return
Figure 8. Digital Keyscan Flow Diagram
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Software
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•
USB API / USB HID
Description
The MSP430 USB API stack is a software solution provided by Texas Instruments that includes
support for:
– Communications Device Class (CDC)
– Human Interface Device class (HID)
– Mass Storage Class (MSC)
– Personal HealthCare Device Class (PHDC)
This software solution, including detailed documentation, is available in the MSP430 USB Developers
Package (MSP430USBDEVPACK).
Files
Src\USB_API\*.*
Src\USB_config\*.*
Src\USB_App\*.*
Ticktimer
Description
Handles a general purpose interrupt timer that is used as a timebase, to wake-up the processor, and to
trigger a new keyboard scan, among other functions.
The ticktimer is implemented using TA0.0 with a default time base of 2 ms.
Files
Src\TI_USBKBD_ticktimer.c
Src\Include\TI_USBKBD_ticktimer_public.h
MSP430 Driverlib
Description
The Texas Instruments MSP430 Peripheral Driver Library (Driverlib) is a set of drivers that provide an
easy mechanism to use the MSP430 peripherals. This software uses Driverlib to initialize the PMM and
UCS modules.
Source code and detailed documentation are available in MSP430Ware (www.ti.com/msp430ware).
For simplicity purposes, this project includes only the pre-compiled libraries for IAR and CCS using a
small memory model and header files.
Files
Src\ driverlib\*.h
Src\ driverlib\driverlib_small_CCS.lib
Src\ driverlib\driverlib_small_IAR.r43
•
•
3.3
Configuration and ScanCode Tables
For modularity purposes and to allow for an easier optimization or upgrade, the USB keyboard software
reserves some Flash sectors for constant tables that define some of the functionality of the application and
define the ScanCode table.
• Configuration Constant Table
Description
Contains the USB keyboard version and configuration constants defining the KeyScan functionality,
such as debounce counter, ticktimer period, etc.
Files
Src\TI_USBKBD_SharedTables.c (declaration)
Src\Include\TI_USBKBD_public.h (typedef)
Declaration
const USBKBD_config_const_t USBKBD_configconst_s
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Location
USBKBD_CONFIGCONST_SEGMENT (0xFC00-0xFDFF)
Contents
Table 5. Configuration Constant Table
Field
•
Size
Description
MagicKey
4 bytes
Indicates the start of the table. 0xDEADC0DE is used by
default.
Version
2 bytes
USB keyboard version in BCD format:
0x0101 - 1.0.1
ticktimer_div
2 bytes
TickTimer divider (based on ACLK):
66 represents a period of 66 / 32768 = ~2 ms
debounce_cycles
2 bytes
Number of debounce cycles in tick counts:
2 represents a debounce of 4 ms with Ticktimer = 2 ms
inactive_timeout
2 bytes
Number of tick counts before going to interrupt_column
mode if no key is detected:
8 represents 16 ms with Ticktimer = 2 ms
ScanCode Table
Description
Contains the USB Keyboard scancode table, mapping each row and column to the corresponding
value based on HID Usage Tables.
Files
Src\TI_USBKBD_SharedTables.c(declaration)
Src\Include\TI_USBKBD_public.h(typedef)
Declaration
const USBKBD_scancodest_t USBKBD_scancodes_s
Location
USBKBD_SCANCODES_SEGMENT (0xFA00-0xFBFF)
Contents
Table 6. ScanCodes
Field
Size
MagicKey
4 bytes
keycode
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Description
Indicates the start of the table. 0xDEADC0DE is used by default.
128 bytes
Keycodes for each key in the following order:
Row0,Col0
Row0,Col1
…
Row0,Col7
Row1,Col0
Row1,Col1
…
Row15,Col6
Row15,Col7
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Hardware and Peripheral Usage
4
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Hardware and Peripheral Usage
In addition to system modules (UCS, PMM), this keyboard implementation uses the peripherals shown in
Table 7.
Table 7. MSP430F550x/5510 Peripheral Usage
Peripheral
Usage
USB
Communication with host (Composite HID-HID)
Timer_A0 (TA0.0)
TimerTick used as a time base to perform periodic polling, debounce, etc.
In addition to the circuitry required for USB and common functionality (reset, VCC, VSS, crystal, etc.), the
USB keyboard uses the pins shown in Table 8.
Table 8. MSP430F550x/5510 Pinout Usage
Columns
KSO0
KSO1
KSO2
KSO3
KSO4
KSO5
KSO6
KSO7
KSO8
KSO9
KSO10
KSO11
KSO12
KSO13
KSO14
KSO15
P2.0
P2.1
P2.2
P2.3
P2.4
P2.5
P2.6
P2.7
P3.0
P3.1
P3.2
P3.3
P3.4
P5.0
P5.1
P5.4
Rows
LEDs
KSI0
KSI1
KSI2
KSI3
KSI4
KSI5
KSI6
KSI7
LED0 (CAPS)
LED1 (NUM)
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
P4.7
P4.6
Schematics showing the implementation on the USB keyboard are found in Section 6.
5
Using the USB Keyboard
When connected to a PC, the USB keyboard should be detected by the operating system and enumerated
without drivers. Windows shows three devices in the Device Manager (see Figure 9).
• Human Interface Devices
– USB Human Interface Device: Standard keyboard in intf0 (MI_00)
– USB Human Interface Device: Custom interface in intf1 (MI_01)
• Keyboards
– HID Keyboard Device: Standard keyboard in intf0 (MI_00)
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Figure 9. USB Keyboard in Windows Device Manager
The keyboard can now be tested and used as a standard keyboard.
In addition to the regular key functionality, the custom interface can be tested using the MSP430 HID USB
Application following these steps (see Figure 10):
1. Select the VID and PID (default: VID = 0x2047, PID = 0x0401).
2. Click Set VID PID.
3. Click Connect.
4. The LED should turn green.
5. Write one of the commands in the Send & Receive field.
6. Observe the response from the USB keyboard.
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Using the USB Keyboard
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3
2
4
1
5
6
Figure 10. Testing the HID Custom Interface
The MSP430 HID USB Application is available in the MSP430 USB Developers Package
(MSP430USBDEVPACK).
5.1
Performance
The usual response time for keyboards is approximately 5 to 50 ms. While this depends on different
factors such as the mechanical implementation of the keyboard, USB bus load, etc., by using this
software, developers have more flexibility to customize the application according to their needs. Whether
response time, price, or power consumption is the most important requirement, parameters such as
debounce time, polling scan rate, USB polling interval, and microcontroller internal frequency can be
adjusted to meet particular requirements.
One important factor affecting the response time is the polling rate, which defines the time required to
scan all keys. While a key press is detected in a few cycles in column-interrupt mode, the algorithm to
recognize the particular pressed key, debounce it, discard "ghost" keys, etc. can take more cycles.
During bench tests, this implementation was measured to take ~1870 cycles (which is equivalent to
~233 µs at 8 MHz) for the first pressed key and ~520 cycles (~65 µs at 8 MHz) for each additional
pressed key.
5.2
Memory Footprint
The following memory footprint was obtained using IAR Embedded Workbench 5.30.4 using the maximum
optimization level:
Code: 7626 Bytes
Constants: 1096 Bytes
Data: 679 Bytes
14
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Schematics
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6
Schematics
R8
R11
1M
10p
C35
10p
C36
KSI5
LED1
LED0
R14
KSI6
4.7M
R15
NC0
R16
IC7
KSI7
4.7M
4.7M
GND
IO1 VCC
6
2
IO2
IO4
5
3
GND IO3
4
TPD4E004
GND GND
4.7u
C39
VBUS
D-
USB1
D- 2
1
D+ 3
GND
D+
4
SHIELD
SBW/Power
SBW_VCC
JP3
14
12
10
8
6
4
2
JTAG1
JP1
int
2
LL103A
D3
1
2
3
ext
1
2
DVCC1
13
11
9
7
5
3
1
SBWTCK
SBWTDIO
VBUS
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
GND
IN
OUT 1
GND NR/FB 3
EN
C20
Q1G$1
3
2
Q1G$2
4
C3
47pF
4MHz
XT2
1
C4 47pF
GND
220n
VBUS_LDO
4.7uF
XT2OUT
XT2IN
C21
10nF
GND
220n
C38
8
4
C11 100nF
GND
V18
VUSB
VBUS
PU.1/DM
PUR
PU.0/DP
VSSU C33
5
LED0
LED1
DVCC1
KSO12
KSO11
KSO10
KSO9
KSO8
KSO7
Digital Keyboard
1uF
GND
R42
JP6
C19
330R
SBWTCK
XT2OUT
XT2IN
AVSS
V18
VUSB
VBUS
PU.1/DM
PUR
PU.0/DP
GND
1
VUSB_VCC
VCC1
SBW_VCC
470nF
VBUS_LDO3
SBWTDIO
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
GND
VCC1
R5
47K
GND
GND
SHIELD1
C8
KSO13
KSO14
KSO15
GP
C9
GND
KSO0
KSO1
KSO2
KSO3
KSO4
KSO5
KSO6
KSI0
KSI1
KSI2
KSI3
KSI4
KSI5
KSI6
KSI7
TP
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
5
6
C13
100nF
33k
DNP
LL103A
D2
R36
GND
+
10uF/6,3V
VBUS
0.1u
C40
GND
C5 C7
100nF
AVCC
GND
1
GND
AVCC
DVCC1
C10
GND
10uF/6,3V
+
R35 27R
R13
4.7M
2
R34 27R
KSI4
4.7M
GND
R19 330R
R18 330R
KSI3
4.7M
R10
1
GND GND GND
KSI2
R7
100R
S3
USB Interface
R6
4.7M
R33
1.4k
PUR
PU.0/DP
PU.1/DM
KSI1
4.7M
VUSB
R3
GND
Digital Keys
KSI0
LED1
GP
KSO7
KSO0
KSI1
KSI7
KSO9
KSI6
KSI5
KSO3
KSI4
KSI2
KSO1
KSI3
KSI0
KSO13
KSO5
KSO2
KSO4
KSO8
KSO6
KSO11
KSO10
KSO12
KSO14
KSO15
Digital Connector
LEDs
GND
LED0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
P$1
P$2
P$3
P$4
P$5
P$6
P$7
P$8
P$9
P$10
P$11
P$12
P$13
P$14
P$15
P$16
P$17
P$18
P$19
P$20
P$21
P$22
P$23
P$24
P$25
P$26
P$27
P$28
P$29
P$30
A
GND
VUSB_VCC
GND
D4
LL103A
Figure 11. Schematics
SLAA514 – December 2011
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USB Keyboard Using MSP430™ Microcontrollers
Copyright © 2011, Texas Instruments Incorporated
15
References
7
References
1.
2.
3.
4.
5.
6.
16
www.ti.com
USB HID specification (www.usb.org/developers/devclass_docs/HID1_11.pdf)
MSP430x5xx/MSP430x6xx Family User's Guide (SLAU208)
MSP430F550x/MSP430F5510 Mixed Signal Microcontroller data sheet (SLAS645)
MSP430 USB Developers Package (MSP430USBDEVPACK) (www.ti.com/tool/msp430usbdevpack).
MSP430Ware (www.ti.com/msp430ware)
Implementing an Ultralow-Power Keypad Interface With the MSP430 (SLAA139)
USB Keyboard Using MSP430™ Microcontrollers
Copyright © 2011, Texas Instruments Incorporated
SLAA514 – December 2011
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