TSS461C datasheet(14/57 Pages) ATMEL

14 / 57 page

TSS461C

4193G–AUTO–12/04

The IFS is defined to be a minimum of 64 prescaled clocks periods. The TSS461C,

accepts an IFS of zero prescaled clocks for the reception only of a SOF sequence.

Once the bus is free, the module must now, if it is an autonomous module emits a SOF

sequence or, if it is a synchronous access module, wait until it detects a preamble

sequence.

Until this point there can be several modules transmitting on the bus, and there is no

possibility of knowing if this is the case or not. Therefore, the first field in which arbitra-

tion can be performed is the identifier field. Since the logical zeroes on the bus are

dominant, and all data is transmitted with the most significant bit (MSB) first, the first

module to transmit a logical zero on the bus will be the prioritized module, i.e., the mes-

sage that is tagged with the lowest identifier will have priority over the other messages.

However it is possible that two messages transmitted on the bus will have the same

identifier. The TSS461C therefore, continues the arbitration of the bus throughout the

whole frame. In addition, if the identifier in transmission has been programmed for

reception as well, it transmits and receives messages simultaneously, right up till the

Frame Check Sequence (FCS). Only then, if the TSS461C has transmitted the whole

message. It discards the message received. Arbitration loss in the FCS field is consid-

ered as a CRC error during transmission.

This feature is called full data field arbitration, and it enables the user to extend the iden-

tifier. For instance, it can be used to transmit the emitting modules address in the first

bytes of the data field, thus enabling the identifier to specify the contents of the frame

and the data field to specify the source of the information.

The identifier field of the VAN bus frame is always 12 bits long, and it is always followed

by the 4-bit command field:

•

The first bit of the command is the extension bit (EXT). This bit is defined by the

user on transmission and is received and retained by the TSS461C. To conform with

the standard, it should be set to 1 (recessive) by the user, else the frame is ignored

without any IT generation.

•

The second bit is the request ACKnowledge bit (RAK). If this bit is a logical one, the

receiving module must acknowledge the transfer with an in-frame

acknowledgement in the ACK field. If it is set to logical zero, then the ACK field must

contain an acknowledge absent sequence.

•

The third bit is the Read/Write bit (R/W). This bit indicates the direction of the data in

a frame.

–

If set to zero it is a "write" message, i.e. data transmitted by one module to

be received by another module.

–

If it is set to one it implies a "read" message, i.e., a request that another

module should transmit data to be received by the one that requested the

data (reply request message).

•

Last in the command field is the Remote Transmission Request bit (RTR). This bit is

a logical zero if the frame contains data and a logical one if the frame does not

contain data. In order to conform with the standard a received frame included the

combination R/W. RTR = 01 is ignored without any IT generation.

All the bits in the command field are automatically handled by the TSS461C, so the user

doesn’t need to be concerned for encoding and decoding these bits. The command bits

transmitted on the VAN bus are calculated from the current status of the active

message.

TSS461C датащи(PDF) 14 Page - ATMEL Corporation

TSS461C датащи(HTML) 14 Page - ATMEL Corporation

Html Pages

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 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

датащи скачать

ссылки URL