DRAGON™ D151
84
Baud Rate, Stop Bits, Parity, Response Timeout, ACK/NACK
Handshake
If these serial parameters are changed using PARAM_SEND, the ACK response to
the PARAM_SEND uses the previous values for these parameters. The new values
then take effect for the subsequent transaction.
Errors
The reader generates a communication error when:
•
The CTS line is asserted when the reader tries to transmit, and is still
asserted on each of 2 successive retries
•
Failure to receive an ACK or NACK after initial transmit and two resends.
SSI COMMUNICATION NOTES
If hardware handshaking is not used, messages should be spaced sufficiently apart,
and the host must not communicate with the reader if the reader is sending.
If hardware handshaking is used, frame each message properly with the
handshaking signals. Do not try to send two commands within the same handshaking
frame.
There is a permanent/temporary bit in the PARAM_SEND message. Temporary
changes are lost when power is removed from the READER. Permanent changes
are written to non-volatile memory. Frequent changes shorten the life of the non-
volatile memory.
Do not scan parameter barcodes and send parameters via SSI simultaneously. All
parameters can be accessed via SSI, so parameter barcode scanning is not
necessary.
Host Interruption
The host can interrupt reader transmission by asserting host RTS. The reader must
detect this, halt transmission, and assert reader RTS (host CTS).
If the host does not transmit at least one byte before de-asserting host RTS the
reader does not detect a transmission (and de-assert to the reader RTS). The reader
resumes the transmission (from where it left off) with the next byte.
If the host transmits (at least one byte) before deasserting host RTS the reader
detects the transmission and does not resume transmission. When the host
deasserts host RTS, the reader begins re-transmitting the data from the beginning.
Summary of Contents for Dragon D151
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