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SA541, SA54L1
PULSE/DTMF SWITCHABLE DIALLERS
FEATURES
■
Selectable Loop-Disconnect (Pulse)
or DTMF (Tone) dialling modes
■
Keypad switchable Loop-Disconnect to
DTMF during a call
■
32 Digit Last Number Redial (LNR)
■
■
Selectable Interdigit Pause (IDP)
500ms or 800ms
Selectable Break:Make Ratios 2:1 or
3:2
■
Operates with inexpensive single contact keypad
Uses inexpensive 560KHz ceramic
resonator
■
On-chip Darlington transistor pair for
DTMF tone filtering
Earth Loop Recall and Timed Break
Recall (Timed Flash)
■
Low on-hook Supply Current options
SA5413 - 5µA @ 2.5V
SA5416 - 1µA @ 2.5V
SA5419 - 1µA @ 3.0V
■
Call, barring/locking feature available
on the SA54L1
■
■
■
Low power CMOS technology enables
direct operation from Telephone line
■
Optional use of external capacitor for
oscillator
PIN CONNECTIONS:
SA541
PIN CONNECTIONS:
SA54L1
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M57-1529
PDS039-SA541-001
REV. B
02-09-94
SA541
ABSOLUTE MAXIMUM RATINGS *
Parameter
Min
Supply Voltage VDD - VSS
-0,3
Voltage on any pin (except HSW)
VSS -0,3
Voltage on pin HSW
VSS -0,3
Current at any pin
-1
(except HSW, FILTOUT and FILTIN)
Current at pin FILTOUT
0
Current at pin FILTIN
-5
Operating Temperature
-25
Storage Temperature
-55
Typ
Max
Unit
6,5
V DD +0,3
1
V
V
V
mA
0,1
0
70
125
mA
mA
°C
°C
Notes
See Note 1
* Stresses above those listed under "Absolute Maximum Ratings" may cause permanent
damage to the device. This a stress rating only. Functional operation of the device at
these or any other condition above those indicated in the operation sections of this
specification, is not implied. Exposure to Absolute Maximum Ratings for extended
periods may affect device reliability.
Note 1: A diode is internally connected between this pin and VDD. Provided current is
externally limited to 300µA max, no damage will occur.
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SA541
DC ELECTRICAL CHARACTERISTICS
(VDD = 2,5V at 25°C, unless otherwise specified)
Condition
Min
Typ
Max
Supply voltage:
on-hook
1,8
5,7
off-hook
2,4
5,7
Hookswitch input: on-hook
0,2 VDD
off-hook
0,8 V DD
Supply Current: on-hook
SA5413
<0.2
5
SA5416
<0.2
1
Sa5419
<0.2
1
off-hook
1,5
MF tone sending
1,0
LD impulsing
200
Output High Voltage
2,2
(MASK, MUTE and IMP Outputs)
Output Low Voltage
0,3
(MASK, MUTE and IMP Outputs)
MF OUT d.c. Level During Tone Sending
0,9VDD
MF OUT Output Resistance
'Key Pressed' Resistance
'Key Not Pressed' Resistance
Darlington Pair Current Gain
3
2
500
600
50,000
Unit
V
V
Notes
For memory retention
µA
µA
µA
µA If MF
mA
µA
V
V
V
kΩ
kΩ
kΩ
VDD = 2.5V
VDD = 2.5V
VDD = 3.0V
OUT is low
I = -1mA
I = +1mA
2,5V<V DD<5,7V
2,5V<V DD<5,7V
Ie=100µA,Vce=2V
AC ELECTRICAL CHARACTERISTICS
(VDD = 2,5V at 25°C, unless otherwise specified)
Condition
Oscillating Frequency
Tone Output: Low Group
High Group
High-to-Low Group Amplitude Ratio
Total harmonic Distortion: 0-4KHz
0-10KHz
0-50KHz
0-200KHz
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Min
68
1,5
Typ
560
77
97
2
1,5
2,5
5,0
6,5
Max
109
2,5
10
Unit
kHz
mVrms
mVrms
dB
%
%
%
%
Notes
No Load
No Load
At MF Out
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SA541
Keypad
R1
R2
R3
R4
C1
C2
C3
Nominal frequency (Hz)
697
770
852
941
1209 1336 1477
Deviation from nominal (%)
-,07
-,10
+,19
-,15
-,17
-,20
-,22
There will be an additional error due to a deviation in the oscillator frequency from 560
kHz.
FUNCTIONAL OVERVIEW
The SAMES SA54X1 is a family of keypad switchable Loop Disconnect (LD)/Dual Tone
multi-Frequency (DTMF) dialler devices for use in low-cost, dual dialling mode telephone
instruments.
The devices feature automatic storage of a single telephone number of up to 32 digits
for Last Number Redial (LNR) purposes. The low current consumption of the SA54X1
ensures memory retention while powered from the line.
Two modes of operation are available. The first is a LD/DTMF mode which operates
normally in LD mode, but can be switched temporarily via the keypad to DTMF mode
during a call. This mode is intended for applications such as home banking, credit-card
verification and other applications requiring low speed data communications. The
second mode allows DTMF dialling only.
The Lock function will be described in the Functional Description.
The SA54X1 is pin compatible with SAMES' SA54X5 family of diallers.
Ordering Information
Lock Option
SA54X1X
L:
with (22 pin package)
Blank: without (20 pin package)
On-Hook Current Option
3
5µA @ 2.5V
6
1µA @ 2.5V
9
1µA @ 3V
4
1µA @ 3V (and TBR Period = 300 mSec)
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SA541
Block Diagram
Figure 1 depicts the SA54X1 block diagram, while Table 1 lists the respective pin
functions.
Figure 1: SA54X1 Block Diagram
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SA541
SA541
Designation
Description
10
SA54L1
10
VDD
Positive Supply input
9
4
9
4
VSS
OSC OUT
Negative Supply input
Connections for 560KHz ceramic resonator
5
12
5
14
OSC IN
MUTE
3
and
6
7
11
1
3
MASK
6
7
13
1
FILT IN
FILT OUT
MF OUT
IMP
2
13
14
15
2
15
16
17
SELECT
C1
C2
C
20
16
17
18
22
18
19
20
C4
R1
R2
R3
19
8
21
8
R4
HSW
-
11
LOCK
Hookswitch input. A logic 1 (High) indicates an “offhook” condition
Lock Input must be tied to VSS to disable all keypad keys
(except TBR, LNR and MUTE). Normal operation is
enabled by connecting LOCK to VDD.
-
12
N/C
No connection
Active high output during keying, tone transmission and
MUTE key depression. (See Note 1)
Output to disable speech circuit during pulse dialling
recall. (See Note 2)
Unity gain amplifier input and output for DTMF tone
filtering
DTMF output
'Loop disconnect' dialling output.
LD/DTMF selection, IDP and B:M ratio programming
Column output connections for 16 button single contact
keypad
Row input connections for 16 button single contact
keypad
Note 1: The MUTE output is provided to disable the microphone while maintaining the
loop condition during DTMF transmission.
Note 2: The MASK output may be used to disconnect the whole speech circuit in order
to mantain the break condition whilst on-hook, during a Timed Break Recall
(TBR) operation or LD dialling.
Table 1: Pin Description
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SA541
FUNCTIONAL DESCRIPTION
Note: All timing data assumes the use of a 560 kHz ceramic resonator as time base.
1. Power On
When power is applied to the chip, a power-on reset circuit operates and ensures that
the Last Number Redial (LNR) store is cleared and all logic is reset. The power-on
reset circuit is designed such that if the chip supply voltage drops to a level at which
the LNR store may be corrupted, it will always, under all conditions, clear the store
when power is restored, so that corrupt data is not retained.
2. Hookswitch Operation
The HSW input is used to inform the SA54X1 of whether the telephone is on-hook
or off-hook. Logic ‘0’ is recognised as on-hook, Logic ‘1’ is recognised as off-hook.
When the HSW input rises from ‘0’ to ‘1’ the off-hook state is recognised immediately
and keypad inputs are accepted. However, when the HSW input falls from ‘1’ to ‘0’
the on-hook state is not recognised for 200-300ms. This ensures that short line
breaks of less than 200ms, such as line reversals applied by the exchange, are
ignored. In this case, the MASK and IMP outputs will go low immediately the HSW
input goes low in order to preserve current, but will resume normal operation
immediately HSW goes high.
On-hook state: In the on-hook state all chip outputs are set low, the oscillator circuit
is inhibited and no key inputs are accepted. This conserves supply current so that
the LNR store contents may be retained.
Off-hook state: When the HSW input goes high, the MASK output immediately
goes to the logic ‘1’ level and remains there until dialling starts (see Figure 5).
COLUMN outputs also go high until a key is pressed. The oscillator circuit remains
inactive until a key is pressed, and is normally off whenever timing functions are not
required, hence reducing operating current.
3.
Keypad Operation
A single contact, normally open keypad is required. When off-hook, the COLUMN
outputs are normally held high and the ROW inputs are low (via internal pull-down
resistors). When a key is pressed, a COLUMN output is connected to a ROW input,
pulling the latter high.
This action initiates keyboard scanning. During keyboard scanning, the COLUMN
outputs are normally low but generate scanning pulses at 7ms intervals on each
output, in sequence. A key is accepted as valid when two successive scanning
pulses from the same COLUMN are seen on a ROW input. Hence, the minimum
bounce-free key closure period which is necessary to guarantee detection is
14ms(plus the oscillator start up time if it was not already running).
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SA541
Simultaneous Key Depressions: If two keys are pressed simultaneously (i.e. a
second key is pressed before the first has been verified), neither key will be accepted
until both keys are released and the correct key is pressed again.
Table 2 indicates the keypad layout for the SA54X1 family.
R1
R2
R3
R4
C1
1
4
7
∗
C2
2
5
8
0
C3
3
6
9
#
C4
TBR
LNR
TBR:
LNR:
Timed Break Recall (Flash)
Last Number Redial
Table 2: Keypad Layout
4.
Dialling Mode Selection
The dialling mode may be selected via the SELECT pin (pin 2) as detailed in Table
3. Four Loop-Disconnect options are available with different Interdigit pauses (IDP)
and Break:Make ratios. If the DTMF mode is selected, dialling will remain fixed in
the DTMF mode. However, if one of the LD modes is selected, the chip will be in
LD mode in the initial off-hook condition, but may be switched to DTMF by pressing
either the ∗ or # keys, provided that dialling is not in progress. If the ∗ or # keys are
pressed during LD dialling, they will be ignored.
Once in DTMF mode, depression of either the ∗ or # keys will cause the relevant
tone-pair to be output. Only digits entered prior to a DTMF switchover will be stored
and available for redialling (see Last Number Redial operation).
Once switched to DTMF, dialling will remain in this mode until either a Recall (Flash)
operation or until the device returns to the on-hook state.
Select (Pin 2)
Connected to:
VSS
C1
C2
C3
VDD
Dialling
Mode
LD
LD
LD
LD
DTMF
IDP(ms)
800
500
500
800
B:M Ratio
2:1
2:1
3:2
3:2
Table3: Dialling Mode Selection
8/16
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SA541
5.
Last Number Redial (LNR)
The function of the on-chip LNR store is to automatically retain a manually dialled
number for redialling later. The capacity of the store is 32 digits. If a number longer
than 32 digits is dialled, redialling will be inhibited.
The LNR store has two features designed to assist the user,viz: Moving Cursor
Facility and Mixed Mode Dialling.
Moving Cursor Facility: This facility is provided to aid use in PABX applications,
where the user must first dial an access digit or digits, and then wait for a second dialtone before continuing dialling.
If the first digits of a new number dialled match the contents of the LNR store, then
pressing LNR button will dial out the remaining digits.
If there is a mismatch in the numbers then redial is inhibited until the next on-hook
and the LNR store will contain the new number.
If the user manually dials the first digit(s) matching those stored in LNR, and then
goes on-hook, the whole contents of the store will be retained.
Mixed Mode Dialling: In the case of a call which starts in LD mode and is switched
by the user (via the ∗ or # keys) to DTMF mode, only the digits dialled in LD mode
will be retained. Provided that the number of digits dialled in LD mode does not
exceed 32, the digits will be retained regardless of the number of DTMF digits
entered subsequently.
6.
Earth Loop Recall (ELR) / Timed Break Recall (TBR) (Timed Flash)
The SA54X1 supports both TBR and ELR and offers a common operating protocol
in both cases.
After a Recall (Flash) operation, the dialling mode selected via the SELECT pin will
be restored. Only the digits dialled after the ELR/TBR operation will be retained in
the LNR store.
A TBR of 100ms (300ms on SA54X14) is generated when the TBR key is pressed.
The MASK output goes low in order to produce the line break. When in DTMF mode,
the MF OUT output also goes low for the duration of the break.
ELR is supported via the C3 pin. If this pin is connected to ground for a minimum
of 20ms during an ELR operation, the chip will offer the same operating protocol as
for TBR.
The ELR function may be achieved by use of the circuit shown in Figure 2, or by use
of a double contact switch.
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SA541
Figure 2: Earth Loop Recall Application
7.
Oscillator Circuit
This requires an external 560KHz ceramic resonator connected between OSC IN
and OSC OUT, providing a timing reference for all chip functions.
Consult your resonator supplier for recommendation of a suitable resonator type.
8.
Tone Filtering
The spectral purity of the DTMF output is sufficient for most applications. However,
where lower distortion DTMF tones are required, an on-chip Darlington pair is
provided (accessible via pins 6 & 7) for use in a low pass active filter.
Figure 3 shows how a 2-pole Sallen and Key filter may be implemented. The typical
component values have been chosen to give a second order Butterworth response
with a cut-off frequency of about 3,5KHz and a nominal pass-band insertion loss of
0,5dB. The relative values of R3 and R4 may be adjusted to achieve the desired
DTMF amplitude which varies with supply voltage.
10/16
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SA541
DTMF Tone Filtering
Figure 3: 2-Pole Sallen and Key Filter Circuit
9.
DTMF Dialling (Figure 4)
During DTMF dialling, the MUTE output goes to logic ‘1’ and remains there for the
duration of the tone transmission. The IMP output remains low during tone
transmission. The MF OUT output rises to its d.c. level of 0,9 VDD at the start of the
tone transmission and is kept there between tone bursts. This is to avoid transients
at the beginning and end of tone bursts.
The maximum rate at which tones are sent to line is 100ms on, followed by 100ms
off. If keys are activated faster than this, they are placed in a temporary store and
then sent to line at the maximum rate. Dialling from the LNR store occurs at the
maximum rate.
If a key is held down for longer than 100ms, the tone output will continue until the
key is released.
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SA541
DTMF Mode Timing Diagram
Figure 4: DTMF Mode Timing Diagram
10. Loop Disconnect Dialling (Figures 5 and 6)
The MASK output is provided in order to disable the speech circuit during LD dialling.
Consequently, the MASK output is normally at logic '1' in the off-hook condition, but
changes to logic '0' during LD dialling. MASK also changes to logic '0' in order to
signal a Timed Break Recall (Flash) to the line. Both MUTE and MF OUT remain
low during LD dialling.
LD dialling is signalled on the IMP output. A break is signalled by a logic '0', make
periods and IDP times are signalled by a logic '1'. When not dialling, the IMP output
remains at logic '0'.
12/16
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SA541
Figure 5: LD Mode Timing Diagram
t1
t2
t3
t4
t5
=
=
=
=
=
Pre-digit Pause (=t5)
Break Period (60ms or 67ms)
Make Period (40ms or 33ms)
Post-digit Make (= t3)
Inter-digit Pause (800ms or 500ms)
Figure 6: Detailed Timing for IMP Output
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SA541
11. LOCKING FACILITY
This feature is available on the SA54L1. Pin 11 (LOCK) should be connected to VSS
if the device is to be locked and to VDD if the device is to be unlocked. This feature
can be controlled by an inexpensive low voltage SPDT switch. When locked,
columns 1,2 and 3 on the keypad are disabled making it impossible to dial out any
digits. However column 4 is not disabled, thus allowing the user to redial the contents
of the LNR store. The user would therefore typically store an emergency number
in the LNR memory before locking the keypad.
TYPICAL APPLICATIONS
The circuit in Figure 7 uses a constant current supply to draw current from the
telephone line which is used to power the SA54X1. The 2,5V reference diode
produces a stabilised supply voltage which determines the DTMF tone level of the
SA54X1.
In Figure 8, a stabilising voltage from the speech circuit is used to supply the SA54X1
during DTMF dialling to give accurate tone levels.
The SA54X1 is powered via the 150KΩ resistor during TBR operations and LD
dialling breaks, and via T1 during dialling makes. This configuration minimises the
component count, at the expense of allowing a leakage current of about 450µA
during dialling breaks. The 47µF reservoir capacitor maintains and smoothes the
supply to the chip.
14/16
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SA541
Figure 7: Typical Application Circuit: Powered via Reference Diode
Figure 8: Typical Application Circuit: Powered via Speech Circuit
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15/16
Disclaimer:
The information contained in this document is confidential and proprietary to South African MicroElectronic Systems (Pty) Ltd ("SAMES) and may not be copied or disclosed to a third party, in whole or in part, without
the express written consent of SAMES. The information contained herein is current as of the date of publication;
however, delivery of this document shall not under any circumstances create any implication that the information
contained herein is correct as of any time subsequent to such date. SAMES does not undertake to inform any
recipient of this document of any changes in the information contained herein, and SAMES expressly reserves the
right to make changes in such information, without notification,even if such changes would render information
contained herein inaccurate or incomplete. SAMES makes no representation or warranty that any circuit designed
by reference to the information contained herein, will function without errors and as intended by the designer.
South African Micro-Electronic Systems (Pty) Ltd
P O Box 15888,
21 Eland Street,
Lynn East,
Koedoespoort Industrial Area,
0039
Pretoria,
Republic of South Africa,
Republic of South Africa
Tel:
Fax:
012 333-6021
012 333-8071
Tel:
Fax:
Int +27 12 333-6021
Int +27 12 333-8071