ACK/NAK are ASCII characters that allow the receiving device to tell the sending device to repeat a data message that contains errors. If enabled, the 3700 expects to receive an ACK (positive acknowledgement of data transmission) or a NAK (negative acknowledgement of data transmission) from the host after each message is sent. If a NAK is received, the 3700 repeats the message. After three attempts to transmit have been made, with successive NAK from the host, the 3700 will discard the message. The 3700 responds to communication from the host with an ACK or NAK.
Pins are available at the I/O Port to support RTS/CTS handshaking. The RTS/CTS feature may be enabled or disabled in the scanner software configuration. During communications, the 3700 will raise RTS and wait for CTS before each transmission. In applications where the host system does not support “handshaking,” the CTS line may be left unconnected and the 3700 will pull it to the active state. Alternately, if CTS is left unconnected, RTS/CTS can be disabled by configuration command.
Preambles and postambles are optional ASCII strings that precede and are appended to each data message sent by the 3700. Typical preamble and postamble strings would include the ASCII control characters STX (start of text), ETX (end of text), CR (carriage return) and LF (line feed). An identification character to indicate the type of bar code read and source scanner port is included in the standard scanner software configuration.
2.4.3Hardwire Pinouts
The following signals not related to communications are available by hardwiring to the motherboard (factory ordered with all cable requirements). See Appendix B for the full lising of available pinouts.
•Pin 1 Boot Strap
•Pin 2 Dig In – Auxiliary
• Pin 3 | Reset |
•Pin 4 IND – Good Read
Auxiliary Trigger
The scanned data input can be controlled by an external triggering device connected to the Trigger/Enable line (pin 2 of the Communications port). The actual trigger can be as simple as a foot actuated relay switch and as sophisticated as an optical sensor.
The Trigger/Enable line action depends on output mode, as follows:
•Bar/Space Output Mode – continuous scan while active
•ASCII Output Mode – read while active – transmit on timeout.
System Hardware Description |