Reader response
#7Done<crc><eom> or #7Error<eom>
For some commands, the Encompass 4 Reader responds with data that relates to the command, such as
T0F 0, to indicate Wiegand mode enabled for a
#532 Display Wiegand Mode Status
command.
#7Error<eom>
will be returned if host transmission is not a legal command with legal data.
Timing and Synchronization
The ECP is largely independent of baud rate. The timeout delays previously described are a function of
baud rate.
The Encompass 4 Reader supports an ECP timeout, which applies equally to both transmit and receive.
The receiver’s minimum timeout delay equals the time to transmit/receive the longest anticipated message
at the current baud rate setting. Additional margin should be included for idle periods between characters;
for example, processing overhead, if any. The timeout delay period can be expressed as follows:
Trec (ms) = L x [Tchar + Tidle]
where
T
char
(ms)
1000 x [ B
c
/ R
b
]
B
c
Bits per character, typically 10
R
b
Baud rate, 1200–38.4 K
L
Length of message in characters
T
idle
Maximum idle period between characters (ms)
Note:
The Encompass 4 Reader supports baud rates between 1200 and 38.4 K.
Likewise, the sender must set a timeout delay equal to the delay of nine characters at the current baud
rate setting. For example, the time required to shift out the
<eom>
character plus the time to shift in the
ACK
or
NAK
message to be received plus a processing allowance for the receiver to process the message
and check for error conditions.
Thus, the sending timeout delay can be expressed as follows:
Tsend (ms) = 9 * Tchar + Terrchk
where
Terrchk (ms)
Processing period to perform error checking by receiver
The host computer can remotely set the Encompass 4 Reader’s communications parameters while in
the command mode, but TransCore does not recommend this action if communications conditions are
marginal.
After the Encompass 4 Reader receives new communications parameters, the Encompass 4 Reader issues
the
Done
message and switches to the new configuration immediately. The host computer switches its
communications parameters immediately after the transaction is complete.
As noted, the message initiator, such as the Encompass 4 Reader in data mode and the host computer
in command mode, starts a timeout counter at the time a message is transmitted. If the timeout expires
Encompass 4 Reader System Guide
TransCore Proprietary.
6–78
Summary of Contents for encompass 4
Page 207: ......
