M-S Cash Drawer A794 - Manual (Page 48)

A794 Owner’s Guide Chapter 5: Communication Interface
December 1999 43
RS-232C Interface
The RS-232C interface uses either XON/XOFF (software) or DTR/DSR (hardware)
protocol to control the flow of information between the computer and the printer. For
XON/XOFF, a particular character is sent back and forth between the host and the
printer to regulate the communication. For DTR/DSR, changes in the DTR/DSR signal
on the RS-232C interface coordinate the information flow.
The RS-232C interface offers the standard settings that are selected through the
Configuration Menu described on page 10 of the “Diagnostics and Configuration”
chapter in the A794 Service Guide.
Print Speed and Timing
The fast speed of the printer requires the application to send data to the printer at least
as fast as it is printed. The application must also allow receipt lines to be buffered ahead
at the printer, so the printer will be able to print each line immediately after the
preceding line, without stopping to wait for more data. Ideally, the application will
send all the data for an entire receipt without pausing between characters or lines
transmitted.
If the application sends data at 9600 baud and pauses between lines for as short a time
as 50 milliseconds, the printer will never be able to print at full speed. However, if the
application sends data at 19.2 K baud and does not pause between lines, the printer will
be able to print at its full speed of 2400 lines/minute. The table below shows that with a
pause of 50 milliseconds after each line, the transmit time equals or exceeds the printer
process time, slowing down the printer, regardless of the baud rate.
50 Millisecond Pause after Each Line
Characters
per Line Lines per
Receipt Transmit Time
(9600 Baud)
in Seconds Transmit Time
(19.2 K Baud)
in Seconds Transmit Time
(115.2 K Baud)
in Seconds Process Time*
in Seconds
20 20 1.40 1.20 1.03 0.50
20 40 2.80 2.40 2.06 1.00
44 20 1.88 1.44 1.07 0.50
44 40 3.76 2.88 2.15 1.00
*Process Time is the time it would take the printer to process the data if all transmitted
data were present. (It is not the time it takes to print the receipt.)
Example: 20 characters/line, with 20 lines = 0.5 seconds process time for the printer. It
takes 1.2 seconds to send the data to the printer at 19.2K baud speed with a 50ms delay
after each line. Thus the printer would have to wait 0.7 seconds longer to receive the
data that it could process it if no delays existed and the transmission speed were faster.