Top N/C (1) [] (2) N/C 0 V (3) [] (4) 0 V +5 V (5) [] (6) +5 V N/C (7) [] (8) +12 V A14 (9) [] (10) A15 A12 (11) [] (12) A13 A10 (13) [] (14) A11 A8 (15) [] (16) A9 A6 (17) [] (18) A7 A4 (19) [] (20) A5 A2 (21) [] (22) A3 A0 (23) [] (24) A1 D6 (25) [] (26) D7 D4 (27) [] (28) D5 D2 (29) [] (30) D3 D0 (31) [] (32) D1 RESET (33) [] (34) M1 BUSRQ (35) [] (36) INT BUSAK (37) [] (38) WAIT WR (39) [] (40) MREQ DR (41) [] (42) IORG N/C (43) [] (44) NSYNC MDIS (45) [] (46) VIDEO 3.2 MHZ (47) [] (48) 4 MHZ Z80 clock 0 V (49) [] (50) 0 V
The expansion port protrudes from the back of the machine into a depression in the casing which protects it. It is part of the CPU printed circuit board and connects directly to the Z80 CPU. Most of the connections are therefore the same as on the CPU and are labelled the same. Care must be taken when the machine is on not to allow anything to short-circuit connections; this is the quickest way to blow your Z80, as is plugging anything on to the port whilst the machine is switched on.
There are many commercial peripherals which have been designed to plug on to the expansion port, of which the most famous is, perhaps, the Amstrad CPS8256 which adds a serial port and a parallel port to the machine. This allows equipment like modems and printers to be added. Other manufacturers have made similar units, sometimes adding extra memory as well.
Other plug-on units are interfaces for scanners, mice and joysticks. Very often the units have a through connection so that several units can be pick-a-backed together. The unit nearest the machine is fixed by two screws, others are secured to it by sticky tape. Not very elegant, but it works.
Some units stick out rather a lot and have no means of positive fixing. Much care must be exercised with these to ensure that they are not dislodged or the CPU and the interface may both be damaged. When moving a machine with this type of interface, make sure that the machine is switched off first, and before switching on ensure that the interface is correctly plugged in. Some of the machines, notably the PcW9256 have the expansion port very low down, and this type of interface was designed to accomodate it.
The expansion port provides a means of communication directly between the CPU and the outside world and can be of great interest to the experimenter.
Ron King
Email address......... ron@king27.freeserve.co.uk