Hand Held Products 3700 CCD manual Scanner/Host Communication, Communications Port

2.4Scanner/Host Communication

The RS–232 communications interface of the 3700 is used for entering configuration commands from a PC or host instrument for specific application requirements. The communications I/O port also sends decoded bar code data to the host.

2.4.1Communications Port

The communications port connector for the 3700 is an 8–pin female modular socket for interfacing to the host system or other communications device. Communications between the host system and the 3700 occur using an Asynchronous ASCII protocol. Refer to Appendix B for a complete description of pin assignments of the RS–232 communications port.

Caution:	Do not use a host communications cable with more wires connected than are
	required for the application. Damage to equipment within the system may result if
	the communications connection is improperly wired.

2.4.2Asynchronous Serial ASCII Interface

The Asynchronous serial ASCII Interface operates in Full Duplex Mode. Software configuration parameters (see Chapter 4) control Baud Rate, Parity, Data Bits, Stop Bits, Xon/Xoff, ACK/NAK, RTS/CTS, and Pre/Postambles.

Baud rate is a means of expressing data transmission speed, where “baud” equals the number of signal events per second (roughly equivalent to bits per second). Parity is a means of checking character bit patterns for validity by confirming if they contain an Even or Odd number of “1”s. The communications port can be configured to operate at baud rates of 600, 1200, 2400, 4800, 9600, 19200, and 38400, with even, odd, or no parity.

Data bits refers to the number of bits used to encode each ASCII character in a data message. Stop bits refers to the number of stop bits appended to each character. The communications port can be configured to send 7 or 8 data bits, with 1 or 2 stop bits.

Note: For proper operation the 3700 must be configured for the same baud rate, parity, number of data bits, and number of stop bits as the connected RS–232 host device.

Xon/Xoff are control characters that refer to ASCII characters “DC1” and “DC3,” respectively. If enabled, Xon/Xoff is a method to control data flow in the following manner. Whenever its buffers approaches full, the device receiving communications data sends an “Xoff” to stop data transmission. The transmitting device stops data transmission. When its buffer approaches empty, the receiving device sends “Xon” and the transmitting device starts sending data again. The receiving device refers to the host instrument. Likewise, the transmitting device refers to the 3700.

Note: The SCANTEAM 3700 will respond to XON and XOFF characters from the host, but will not send these characters.

2–4 System Hardware Description