TransCore encompass 4 - Switch to Command Mode Request

Communications Protocols
6-7
The host computer resets the anticipated data message sequence
number to that of the Encompass 4 Reader before
communications can resume without error.
<ack/nak> ASCII @ character for ACK response; ASCII ? character for NAK
response
<crc> CRC value for the message
<eom> End-of-message character (ASCII CR)
The Encompass 4 Reader sets a user-programmable timeout delay at the time each
message is transmitted based on command #612NN Set Error Correcting Protocol
Timeout, where NN = timeout delay. To disable the timeout delay for diagnostic pur
-
poses, issue the command #612FF Disable Error Correcting Protocol Timeout.
If the timeout delay expires before the Encompass 4 Reader receives an ACK or NAK
message from the host, a logical NAK condition will be declared. If the Encompass 4
Reader receives a NAK or timeout, the reader retransmits the data message.
When the Encompass 4 Reader receives an ACK message, the system software treats
the message as having been properly received by the host. The software increments
the sequence number, and advances pointers to the next message in the Encompass 4
Reader’s message queue to prepare for sending the next message.
Switch to Command Mode Request
The host computer may issue command #01 Switch to Command Mode while in data
mode.
The basic protocol format is as follows:
<som><cmd><eom>
The ECP format is as follows:
<som><seq><cmd><crc><eom>
where
<som> Start-of-message (ASCII # character)
<seq> Sequence number generated by the host computer separately
from that appearing in data messages transmitted by the
Encompass 4 Reader
<cmd> Switch to command mode (ASCII characters 01)
<crc> CRC value for the message
<eom> End-of-message character (ASCII CR)