CPC Guide - Controlling the PrinterPrinter Control
The printer is controlled using port &EFxx and port &F5xx of the 8255 PPI.

The ready status of the printer is controlled by checking bit 6 of port &F5xx. 
If the printer is on-line, this bit will be set to 1, if it is offline this bit 
will be set to 0.

Data may be sent to the printer by using port &EFxx. (This port cannot be read.)

The user may only send 7 bit values. The 8th bit is used as the strobe. This is 
like a flag telling the printer that data is ready, it is a peak, as shown in 
the diagram below:

The strobe looks like this:


       +---+
       |   |
_______|   |_________

The user must send a 0 on the strobe bit, then a 1 and then a 0. The printer 
will then take the byte and print it. (At all times the data that you want the 
printer to take and print, should be present on bits 7-0.)

NOTE:

When the computer is switched on or reset, the strobe bit is set to 0.




Making a printer lead
What you need
  34-way ribbon cable 
  34-way edge connector (for CPC's with edge connectors) 
  A 36-way centronics D type male edge connector 
Attach the edge connector to one end of the ribbon cable, and the D-type 
connector to the other end of the ribbon. When you connect the D-connector you 
will see 2 columns of pins which are not used. Make sure that pin 1 of the edge 
connector connects to pin 1 of the D-type connector. 

There is a problem with the CPC printer lead. When you try to print something 
out extra lines (carriage returns) are generated, and so the text comes out as 
if it was double spaced. To solve this is easy, just cut the wire in the ribbon 
cable for pin 14 (see the wiring diagram for the printer interface because it 
doesnt follow normal ribbon cable numbering patterns). 


Summary

Bit 7   Centronics Strobe
        1: Activate strobe

Bit 6   Data bit 6
Bit 5   Data bit 5
Bit 4   Data bit 4
Bit 3   Data bit 3
Bit 2   Data bit 2
Bit 1   Data bit 1
Bit 0   Data bit 0




Programming examples
a) Checking the printer is on-line,
LD B,&F5                        ;8255 PPI Port B

.not_on_line
IN A,(C)                        ;get byte from port
and %01000000                   ;isolate bit indicating printer
                                ;on-line status

jp z,not_on_line

RET




b) Sending a byte to the printer,
LD B,&EF                        ;Printer data port

AND %01111111                   ;make sure bit 7 is set to 0.
OUT (C),A                       ;send byte to printer

                                ;low part of diagram

OR %10000000                    ;make sure bit 7 is set to 1.
                                ;(Activate strobe).
OUT (C),A                       ;send byte

                                ;peak of diagram

AND %01111111                   ;make sure bit 7 is 0.
OUT (C),A                       ;send byte again

                                ;low part of diagram

RET                             ;and end