The CPC Printer Port has only 7 bit data. Which is sufficient for english 7 bit ASCII character sets, but not enough for 8 bit character sets. Also, printing bitmap graphics usually requires 8 bit data (though usually can also print 7 pixels columns combined with a reduced line-feed rate). Amstrad's DMP1 works perfectly with 7 bit, but Amstrad's later DMP2000/DMP2160 include a few functions that won't work on 7 bit ports - so even the official CPC printers aren't fully compatible with the CPC printer port.
Internal 8 bit Printer Ports/Mods
Happy Computer 8 bit Printer Port upgrade (DIY)
A good method to upgrade to full 8 bit has been described in the german magazine "Happy Computer (Schneider Sonderheft) 2/85 and 4/86":
- Disconnect the D7 pin from ground, and wire it to the PIOs Tape WR DATA pin instead (That is, Pin 12 of the 8255 chip).
Sharing that pin will cause no problems (as long as you do not attempt to send data to the tape drive and to printer at the same time). Of course, you will also have to customize your software, or BIOS ROM, or the BIOS jump vectors in RAM, in order to take advantage of the modification. In contrast, this DIY is supported by FutureOS.
- For details see: Happy Computer 8bit Printer Mod
CPC Schneider International - 8 bit Printer Port Mod
DIY from CPC Schneider International (issue 12'85, page 64), this solution uses joystick port pin 8 (or (keyboard?) pin 2, unclear?).
- For details see: CPCI 8bit Printer Mod
PC Amstrad International - 8 bit Printer Port Mod
DIY from PC Amstrad International (issue 8/9'91, page 69-70), this solution uses PPI.Pin12 (same as the Happy Computer 8bit Printer Mod).
8 bit Printer Port in KC Compact
The KC Compact uses the bit 5 of PPI Port C as 8th printer bit (this is same as the Happy Computer mod, see above). Although the 8th bit is a built-in feature, the KC Compact Firmware doesn't support it. But it's supported by FutureOS.
8 bit Printer Port in Aleste 520EX
The Aleste 520EX includes an 8bit printer port, using PSG Ext Port B for data (which does not exist on the CPC), and PPI port C, Bit 4 for strobe (which would be Tape Motor in CPC). The Aleste doesn't have the normal CPC-style Printer Port at Port EFXXh. The BIOS functions are patched accordingly; including for supporting the 8th bit (unlike the CPC Plus and KC Compact, which do not support the 8th bit in BIOS functions).
8 bit Printer Port in CPC Plus
In the CPC Plus, Bit 3 of CRTC Register 0Ch can be used as eighth printer bit. For compatibility to normal CPCs, this feature can be disabled by removing the 10 kOhm resistor R30 on the mainboard (aka R130 in the schematic). See LK Links for more info. Although the 8th bit is a built-in feature, the CPC Plus Firmware doesn't support it. However the 8 bit printer port of the CPC Plus is supported by FutureOS.
External Printer Ports
- 8bit Printer Port (Amstrad Action) (DIY) - connects to Expansion Port (uses Port FBF8h/FBF9h)
- 8bit Printer Port (Paul Bauriedl) (DIY) - connects to Printer Port (splits port EFxxh to 2 x 4 bit)
- BrunWord's Eight Bit Status port - connects to Printer Port (splits port EFxxh to whatever, details are unknown)
- CPCI 8bit Printer Mod (DIY) - connects bit 7 to Joystick_1_Select signal (can be connected internally or externally)
- CPCISA by Yarek can be used with various ISA bus printer cards (8bit, one- or bi-directional types, SPP, XPP, EPP, etc.)
- KDS 8-Bit Printer Port (KDS Electronics) - connects to Printer Port (splits port EFxxh to whatever fragments - details are unknown)
- Panda Electronics Communications Interface Unit (dual RS232 plus PPI-based 8bit printer port) (Panda Electronics Ltd)
- RS232 Interfaces (various manufacturers) - can be used to access RS232-compatible printers with full 8 bit support
- Schneiderware Centronics Port - connects (via a separate motherboard) to Expansion Port (uses a 8255 PPI chip)
Also, reportedly, the following external hardware exists:
- 8 bit Printer Port (Pride Utilities) (details)
- 8 bit Printer Port with Dual RS232 (Timatic Systems)
- 8 bit Printer Port with 16 bit I/O port (HoneySoft) (see advert)
Other external printer-related hardware (though not 8bit related):
- Centronics to serial 8-pin DIN Adaptor for "Gabriele 9009" daisy-wheel printer from Triumph-Adler (DIY, CPC Schneider International 12-1985, pages 88, 89)
- KDS Printer T Switch (KDS) - allows to connect 2 printers, the desired printer can be selected via software