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ACK/NACK Control
5-9
ACK/NACK Control
5-9-1 Error Handling in ACK/NACK Control
When using ACK/NACK control, if the host does not receive a normal response, the Controller will
resend the response by either (1) when the host sends a NACK command to the Controller or (2)
when there is no response within a set period of time. Consequently, a response can be received
without communicating with a Tag again. The host checks that responses have been received nor-
mally using the ACK/NACK commands, so response data can be communicated dependably.
Using ACK/NACK Control
If the host receives a normal response, it sends an ACK command to the Controller. The Controller
judges that the host has received a normal response, and enters a command-waiting state. If, after
the Controller has sent the response, an ACK is not received normally within the time set using the
time out setting, or a NACK is received, the Retry Flag is set and the last response is sent again.
The maximum number of response retries that can be made is nine.
(1)
Host Receives a Normal Response and Sends ACK Command
Host
Controller
(2)
Host Cannot Receive a Normal Response and Sends a NACK Command
Host
Controller
(3)
Host Did Not Send an ACK/NACK Command within the Timeout Period
Host
Controller
5-46
Command
ACK
Response
Command
NACK
Response
Error occurs
Command
Response
Timeout
ACK
Response
Retry
ACK
Response
Retry
Section 5-9
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