Epson 4100 manual Hardware Handshaking, Busy Inverse DTR

B-16 Appendix B—Serial Interface

HARDWARE HANDSHAKING

Hardware handshaking controls data transmission by changing the voltage level on a signal wire. Not all printers can respond to control characters embedded in the data stream (software handshaking).

Many printers use a pin on the connector to specify a "buffer full" condition. When the printer asserts its buffer-full line, data transmission stops.

The printer supports two hardware handshaking protocols:

•DTR

•BUSY (Inverse DTR)

DTR

DTR handshaking protocol uses the DTR signal on Pin 20. The voltage remains high until the print buffer is 256 bytes from full, at which time DTR is set low. When the buffer is 2256 bytes from full (257 bytes if minimum buffer size is selected in the configuration menu), DTR resets to high and data transmission can resume.

BUSY (Inverse DTR)

DTR is specified for Pin 20 of an RS-232-C serial interface. Used according to RS-232-C specifications, DTR is high when the printer is ready to receive new print data, and low when it is busy processing print data.

On the 4100 printer, DTR on Pin 20 is also wired to Pins 11 and 19. Some computer operating systems expect a signal called BUSY (or inverse DTR) on either Pin 11 or 19, in place of DTR. If used, BUSY is low when the printer is ready to receive new print data, and high when it is busy processing data. This is directly opposite of DTR.