TSS463 ATMEL Corporation, TSS463 Datasheet - Page 47

• Manufacturer Part Number: TSS463
• Description: VAN Data Link Controller with Serial Interface
• Manufacturer: ATMEL Corporation

Retries
Rearbitrate
Typical Example
4102E–AUTO–12/04
The purpose of the retries feature is to provide, for the user, the capability of retrying a
transmit request in case of failure, when a node tries to reach another node, either on
normal DATA frame or on REPLY REQUEST frame.
The maximum number of retries is programmable through MR[3:0] of the Transmit Con-
trol Register (0x01). When a channel is enable - bit CHTx = 0 of Message Length and
Status Register, a 4-bit counter is loaded with MR[3:0]. At each attempt, this counter will
count-down to 0, an IT TE is set in the Interrupt Status Register (0x09), and the trans-
mission is stopped.
MR[3:0] = 1 indicates 1 retry, hence 2 transmission attempts will be performed (see
Table 5, “Retries,” on page 28). The number of retries performed, as well as the current
channel number associated, can be read in the Transmission Status Register (0x05).
The Last Error Status Register (0x07) informs about the trouble uncounted:
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There is only one retry counter for all channels. When the user writes the Max_Retries
value, all channels start their transmission with this parameter.
The purpose of rearbitrate feature is to postpone a channel already in transmission in
order to authorize an higher priority (see Section "Priority Among the Different Chan-
nels", page 46) message to be transmit.
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Failure cases:
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It should be noticed that contention is considered as normal CSMA/CD protocol
and, therefore, is not taken into account in failure cases. So, an 'infinite' number of
attempts can be performed if bus contention occurs continuously.
Max_retries = 1 (2 transmissions attempts).
If Ch8 is in a the retry loop and the user wants to transmit the Ch5 without waiting
the end of the loop, the user can use the rearbitrate command.
The TSS463B will then wait until the end of the current transmission, reload the
retries counter and enable the Ch5 to transmit.
At the end of this transmission Ch5, either when the attempt is successful or the
exceeded retry count is reached, the retries counter is reloaded and the
transmission is activated for the Ch8 again.
Code viol (CV error bit)
Acknowledge error (ACKE error bit)
CRC error (FCSE error bit)
TSS463B
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