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Appendix A System Interface Description Appendix A System Interface Description
A-7 A-8
Additional Information 3 Parallel Centronics Interface
After Power-ON DTR and RTS are activated and the printer is ready to receive
data. Interface Characteristics - Connector pin assignment / signal definition
XOFF is sent, when the interface buffer has only space left for 256 more charac-
ters. XOFF is sent again, at a level of 128 characters buffer space. Further
incoming data will be stored until the interface buffer is full. All data sent in
addition will get lost.
XON is sent when the interface buffer provides space for a minimum of 512
characters.
XON/XOFF can only be sent successfully when CTS and (DSR) is at active
state.
XOFF will be sent immediately if local mode is entered.
XON is sent again, if local mode is left and a minimum of 512 byte interface
buffer is available.
®
Signal Description line Pin
Pin No. Return Direction
No.
_______ Control Signal from the Host. 1 19 Input
STROBE Printer reads data line (Data 1 to Data 8) when
*)
going low.
Data 1 - 8 Data lines transfer the characters from the host to 2 - 9 20 - 27 Input
the printer. Data 8 = most significant bit.
_____ Acknowledge - Control signal from the printer. Logi- 10 28 Output
ACKN cal 0 indicates that the printer has received a print/-
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control character and is ready for the next data
transfer.
BUSY Control signal from the printer. Logical 1 indicates 11 29 Output
that the printer is unable to receive any more
data.
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PE Paper Empty - Control signal from the printer. This 12 -- Output
signal goes high when paper runs out, i.e. load
upper or lower tractor, paper jam.
SELECT Control signal from the printer. Always logical 1. 13 -- Output
Indicates that the printer is ON-LINE and ready.
LG Logic Ground 14 --
-- not used 15 --
LG Logic Ground 16 --
CG Chassis Ground 17 --
VCC + 5 volt 18 --
SG Signal Ground 19 - 30 --
____ Control signal from the host. Does not reset the 31 -- Input
INIT printer but generates an acknowledge pulse (logical
*)
1).
______ Control signal from the printer. Always logical 1. If it 32 -- Output
FAULT goes to logical 0 the printer has been switched off.
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LG Logic Ground 33 --
-- not used 34 - 36 --
Overlined signal names indicate that the signal is true when the signal level is
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low.
When the interface buffer is full except for the last character, BUSY will not be
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reset. BUSY will be reset when space is available again for least 256 charac-
ters in the interface buffer. While the printer is offline (Stop Mode) BUSY
remains active until the printer enters the online state again.