ib technology

5

Command Protocol

The commands are described fully in the following pages. The STATUS, MESSAGE and

PROGRAM EEPROM commands are common to all the Reader modes, the structure and

reply from commands such as READ PAGE can be different depending on which Reader

mode is selected. Generally, command codes (plus optional data bytes) are transmitted to the

RWD which replies with an Acknowledge byte (and data bytes if appropriate). The

Acknowledge code should be read back by the host and decoded to confirm that the command

was received and handled correctly. The serial bit protocol is 9600 baud, 8 bits, 1 stop, no

parity (lsb transmitted first).

The status flags returned in the Acknowledge byte are as follows:

b7 b6 b5 b4 b3 b2 b1 b0

1

1

1

1

1 1 1 1

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EEPROM error (Internal EEPROM write error)

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| Tag OK (Tag identity code matched to list)

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| Rx OK (Tag communication and acknowledgement OK)

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RS232 error (Host serial communication error)

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RELAY Enabled flag

HTRC (or Antenna fault) error flag

Note that bits 6 and 7 are fixed 1’s so that an acknowledge code of CO (Hex) would indicate

NO valid transponder in the RF field, whereas an acknowledge byte of D6 (Hex) would

indicate a correctly matched transponder detected in the field (and no errors).

Note also that only the relevant flags are set after each command as indicated in the protocol

documents.

NOTE:

1) The serial communication uses hardware handshaking to inhibit the host from sending

the Micro RWD commands while Tag interrogation is in progress.

2) Following the Read Tag command, if an error flag has been set in the Acknowledge

code then there will be NO data.

3) The serial communication system and protocol allows for a 10ms ‘window’ every Tag

polling cycle indicated by the BUSY line being low. During this ‘window’ the host

must assert the first start bit and start transmitting data. The BUSY goes high again

10ms after the last stop bit is received.

4) NOTE that only one command sequence is handled at a time.

Tag STATUS

Command to return Tag status. The acknowledge byte flags indicate general Tag status.

B7

B0

Command:

0 1 0 1 0 0 1 1

(ASCII “S”, 0x53)

Acknowledge:

1 1 F F F F F X

(F = Status flags)