TransCore IT241005422 Manual De Usuario

<seq #>

 - a combination of 

<seq #>

 and 

<len>

, makes 16 bits or 2 bytes of data. 

The sequence number is 6 bits and the length is 10 bits. The sequence number is used 
for the error detection scheme. The value for sequence number may represent any 
number between 0 and 63. The sequence number for the acknowledge (ACK)/not 
acknowledge (NACK) message matches the sequence number of the last received 
message.

<len>

 - length is a group of 10 binary bits that specifies the number of bytes in the 

response. The value of length is 1 for ACK/NACK responses.

<resp>

 - response is 1 byte long to indicate the status of the data response received 

by the programmer from the host. Table D-3 lists the responses.

<crc>

 - cyclic redundancy check, or CRC, is 2 bytes, or 16 binary bits long, denoting 

a CRC-XMODEM result generated on each message byte exclusive of the 

<som>

 and 

<eom>

. The polynomial for the CRC calculation is X

16

+X

12

+X

5

+1 with a feedback of 

1021H for a XMODEM type CRC.

<eom>

 - end of message aids in finding the end of the message. All data after the 

<eom>

 is ignored until the next 

<som>

 is detected. The end of message is defined as 

the ASCII character

 

%

.

Tag data or diagnostics data generate asynchronous or command responses. Asyn-
chronous responses have no associated commands. An interrupt occurs notifying the 
lane controller or host computer of a response to read data from the first-in-first-out 
(FIFO) data I/O address if interrupt mode is enabled. Otherwise, polling the FIFO 
buffer status register notifies the lane controller or host computer to asynchronous 
responses. The reader and host interface use the communications protocol for com-
mand responses and asynchronous responses shown here. Binary-coded integer mes-
sages contained in a protocol are defined by:

<len> <resp> [<data>]

where

<len>

 - length specifies the number of bytes in the response and data fields. The 

range for this field is 2 to 1022.

<resp>

 - response is one-word long to indicate the status of the command received by 

the host from the reader. The responses are shown in Table D-4.

DDH

Data acknowledge (ACK)

EEH

Data invalid (NACK)