AMIS-30660 Minimum Communication Speed

AND8379/D
AMIS-30660 Minimum
Communication Speed
http://onsemi.com
APPLICATION NOTE
Introduction
Measurement Setup
The AMIS−30660 is designed for high speed CAN
transmission. This means that communication up to 1 Mbps
is guaranteed. The minimum speed is defined by the TxD
dominant time−out and the used symbol length in the
protocol. The CAN protocol ensures, that no more than 5
identical consecutive bits occur in an error−free bit stream.
However, in a situation when an error shall be flagged on the
bus, up to 12 consecutive dominants (logical 0’s) can be
encountered. If the symbol length is 12 bits, the minimum
speed is 48 kbps.
Figure 1 shows the measurement setup used to determine
the minimum speed of operation:
• A high speed AMIS−30660 CAN transceiver is
connected through a terminated CAN network to a
second AMIS−30663 CAN transceiver.
• A generator is sending a square wave signal with 5 V
amplitude and varying frequency in the TxD pin of the
first CAN transceiver.
• With a four−channel oscilloscope TxD, CANH, CANL,
and RxD of the second transceiver is monitored.
+5V
VCC
TxD
VREF
RxD
7
CANH
CANH
1
AMIS−30663 5
6
GND
8
7
5 AMIS−30660
4
V33
3
1
2
Generator
VCC
3
CANL
CANL
60 W
8
60 W
47 nF
S
6
4
2
PC20040713.1
TxD
VREF
RxD
GND
Figure 1. Measurement Setup
Observation
transmission of the dominant level (CANH = high and
CANL = low) is ceased after a time−out period. This
time−out is the maximum low time at the RxD pin. As
illustrated below the measured maximum (RxD) dominant
time is 391 ms.
When the frequency of the square wave signal at the TxD
pin is gradually decreased, the signal at the RxD of the
second transceiver is also lowered in frequency. Below a
certain frequency the duty cycle starts to be effected. The
© Semiconductor Components Industries, LLC, 2009
January, 2009 − Rev. 2
1
Publication Order Number:
AND8379/D
AND8379/D
Figure 2. Measurement Result
Explanation
In Table 1, taken from the AMIS−30660 data sheet, there
is a time−out for dominant TxD signaling. This prevents the
bus−lines being driven to a permanent dominant state
blocking all network communication.
Table 1. TIMING CHARACTERISTICS; AMIS−30660 DATA SHEET, PAGE 9
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
VTXD = 0 V
250
450
750
ms
TIMING CHARACTERISTICS (see Figures 6 and 7)
tdom(TXD)
TXD dominant time for time out
The typical value indicated in the datasheet is 450 ms. To
calculate the minimum transmission speed the minimum
value (250 ms) needs to be taken. This yields in:
f TxD,min +
The practically usable baud rate is defined as the
theoretical minimum bit−rate multiplied by the maximum
symbol length.
If the symbol length was 1 bit, which means that the
maximum dominant state length is one bit−time, the
minimum speed would be 4 kbps. If 12 consecutive zero’s
are allowed – as it’s the case for the CAN protocol, or the
symbol length is 12 bit, than the minimum speed is 4 x 12 =
48 kbps.
1
1
+
+ 4 kHz
t dom,min
250 ms
This means that the minimum theoretical bit−rate is
4 kbps provided that no more than 1 dominant (logical 0) is
transmitted in a row.
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All
operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights
nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
P.O. Box 5163, Denver, Colorado 80217 USA
Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada
Email: [email protected]
N. American Technical Support: 800−282−9855 Toll Free
USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81−3−5773−3850
http://onsemi.com
2
ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your local
Sales Representative
AND8379/D
Similar pages