PSC Scanners Serial Commands

Serial Commands

Serial Commands are only accepted by the PSC scanner when in

serial communications mode.

Serial commands take the form: STX ESC LT1 LT2 <optional param-

eters>ETX (Note: STX = ^B; ETX = ^C)

STX, ESC, and ETX are ASCII codes whose values are 02H, 1BH, and

03H, respectively. LT1 and LT2 are uppercase ASCII letters (commer-

cial A and @ are the same as those printed in earlier sections of this

manual under their corresponding menu bar code labels). The ESC

code that follows the STX code identifies this as a command. Some

commands require parameters such as minimum and maximum code

lengths, and strings of hexadecimal characters. When parameters are

required by the command, they immediately follow LT2. There are

never spaces within serial commands.

The scanner provides ACK/NAK protocol during serial program-

ming in order to provide feedback to the host computer which is pro-

gramming the scanner.

ACK/NAK protocol provides two vital functions. First, it provides

the host with positive acknowledgment that its commands are being

accepted and acted upon. Second, and perhaps more important, it

ensures that the host will not issue commands to the scanner more

quickly than the scanner can process them. For example, every time

the scanner receives a correct command, it modifies its internal

EEPROM, a function that takes about one second. At 9600 baud, the

host can easily issue commands to the scanner faster than they can be

processed. If after issuing each command the host waits to receive an

ACK or NAK code before issuing the next command, the scanner

cannot be overrun. If XON/XOFF or CTS/RTS Protocol is being used,

the scanner cannot be overrun by programming commands. How-

ever, the host is not provided with feedback as to the outcome of its

commands.

The ACK/NAK protocol is quite simple. Whenever the scanner

receives a correctly formatted command, it sends a confirmation mes-

sage followed by an ACK (06H) code.