TSS463B datasheet(47/59 Pages) ATMEL

47 / 59 page

TSS463B

4102E–AUTO–12/04

Retries

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:

•

Failure cases:

–

Code viol (CV error bit)

–

Acknowledge error (ACKE error bit)

–

CRC error (FCSE error bit)

•

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.

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.

Rearbitrate

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.

Typical Example

•

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.

TSS463B Datasheet(PDF) 47 Page - ATMEL Corporation

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