Rice Lake Motorola DS457 Laser Scanner - Manual (Page 157)

Serial Interface 9 - 11
Hardware Handshaking
The data interface consists of a serial port designed to operate either with or without the hardware
handshaking lines
Request to Send
(RTS) and
Clear to Send
(CTS).
If Standard RTS/CTS handshaking is not selected, scan data transmits as it becomes available. Select
Standard RTS/CTS handshaking to transmit scan data according to the following sequence:
•
The imager reads the CTS line for activity. If CTS is asserted, the imager waits up to the Host Serial
Response Time-out for the host to de-assert the CTS line. If, after the Host Serial Response Time-out
(default) the CTS line is still asserted, the imager sounds a transmit error and discards any scanned data.
•
When the CTS line is de-asserted, the imager asserts the RTS line and waits up to the Host Serial
Response Time-out for the host to assert CTS. When the host asserts CTS, data transmits. If, after the
Host Serial Response Time-out (default) the CTS line is not asserted, the imager sounds a transmit error
and discards the data.
• When data transmission completes, the imager de-asserts RTS 10 msec after sending the last character.
• The host responds by negating CTS. The imager checks for a de-asserted CTS upon the next
transmission of data.
During data transmission, the CTS line should be asserted. If CTS is deasserted for more than 50 ms between
characters, the imager aborts transmission, sounds a transmission error, and discards the data.
If the above communication sequence fails, the imager issues an error indication. In this case, the data is lost
and must be rescanned.
If hardware handshaking and software handshaking are both enabled, hardware handshaking takes
precedence.
• None
: Scan this bar code to disable hardware handshaking.
• Standard RTS/CTS
: Scan this bar code to select Standard RTS/CTS Hardware Handshaking.
• RTS/CTS Option 1
: The imager asserts RTS before transmitting and ignores the state of CTS. The
imager de-asserts RTS when transmission completes.
• RTS/CTS Option 2
: RTS is always high or low (user-programmed logic level). However, the imager waits
for CTS to be asserted before transmitting data. If CTS is not asserted within Host Serial Response
Time-out (default), the imager issues an error indication and discards the data.
• RTS/CTS Option 3
: The imager asserts RTS prior to any data transmission, regardless of the state of
CTS. The imager waits up to Host Serial Response Time-out (default) for CTS to be asserted. If CTS is
not asserted during this time, the imager issues an error indication and discards the data. The imager
de-asserts RTS when transmission completes.
NOTE
The DTR signal is jumpered to the active state.