Epson A794-D100 manual RS-232C Interface, Print Speed and Timing

A794 Owner’s Guide Chapter 5: Communication Interface

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.

The table shows that with a pause of 50 milliseconds after each line, the transmit time equals or exceeds the print time, slowing down the printer, regardless of the baud rate.

50 Millisecond Pause after Each Line

Characters	Lines per	Transmit Time	Transmit Time	Transmit Time	Process Time*
per Line	Receipt	(9600 Baud)	(19.2 K Baud)	(115.2 K Baud)
20	20	1.4 Sec.	1.2 Sec.	1.03 Sec.	0.5 Sec.
20	40	2.8 Sec.	2.4 Sec.	2.06 Sec.	1.0 Sec.
44	20	1.88 Sec.	1.44 Sec.	1.07 Sec.	0.5 Sec.
44	40	3.76 Sec.	2.88 Sec.	2.15 Sec.	1.0 Sec.

*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.

The next table shows that with no delay between lines, the transmit time is much less than the process time, allowing the printer to print at full speed.

No Delay Between Lines

Char. per	Lines per	Transmit Time	Transmit Time	Transmit Time	Process Time
Line	Receipt	(9600 Baud)	(19.2 K Baud)	(115.2 K Baud)
20	20	0.4 Sec.	0.2 Sec.	0.035 Sec.	0.5 Sec.
20	40	0.8 Sec.	0.4 Sec.	0.07 Sec.	1.0 Sec.
44	20	0.88 Sec.	0.44 Sec.	0.075 Sec.	0.5 Sec.
44	40	1.76 Sec.	0.88 Sec.	0.15 Sec.	1.0 Sec.

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