5-5
Section
ACK/NACK Control
77
If the single repeat, FIFO repeat, multiple trigger, or multiple repeat option is spe-
cified for communications with the ID Tag, multiple responses will be returned for
a single command.
Host
Controller
Command
Response
Response
Response
Response
5-5
ACK/NACK Control
When ACK/NACK control is being used and the host was not able to receive a
response normally, it is possible to receive a response even if communications
with the Tag are not executed again. ACK/NACK control verifies that the host
received the response normally, so response data communications can be per-
formed reliably.
Use of ACK/NACK Control
The Controller returns a response for a command sent from the host and the
host sends ACK when the response to the command is received. Then the Con-
troller determines that the host has received the response normally and waits for
the next command. If the Controller does not receive ACK within a preset time-
out period or the Controller receives NACK, the Retry Flag is set and the re-
sponse is returned to the Controller again. This is repeated at least nine times.
The host receives a response normally and sends ACK.
Host
Controller
Command
Response
ACK
The host sends NACK because a response is not received normally.
Host
Controller
Command
Response
NACK
Error results
Response
ACK
Retry
The host does not send ACK/NACK within a preset time-out period.
Host
Controller
Command
Response
Time out
Respons
e
ACK
Retry
Multiple Responses
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