Citizen Systems CBM-290 - Manual (Page 29)

CITIZEN 29
7.2 Explanation of Input / Output signals
7.2.1 Input / Output signals
(1) RD
Serial receiving data signal. On occurrence of framing error, overrun error, or parity error,
the data is printed as "?".
(2) DTR
When this signal is READY, write data or a command. When they are written in BUSY,
overrun error is occurred and data is ignored. Even during printing, data can be loaded in
the input buffer. Further, BUSY can take place on supply of power, during test printing,
during on-line, or on resetting.
(3) TD
When, while in data reception, the rest of input buffer on the printer side goes less than
128 bytes , DC3 (13H) data reception impossible signals are output.
When the rest of input buffer goes more than 256 bytes, DC1 (11H) data reception possible signals
are output to the host. When DTR/DSR control having been selected in status
information transmission, it is first confirmed that DSR is "space" and data is sent.
When DTR/DSR control has not been selected, DSR is ignored and data is transmitted.
(4) FG
Case GND
(5) GND
Common GND on the circuit.