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The Sharp display code set presents 256 characters defined in a ROM on a 8 x 8 matrix ( 64 dots per character ). If, through hardware alteration, you replace part of this ROM by RAM it becomes possible to define your own characters. This mod allows the user to define 128 characters, display codes 128 to 255, whilst codes 0 to 127 remain unaltered. It is also possible by a switch to return to the normal character set. The system works from 3 memory ports with addresses E014 Hex, E015, E016. E014 is used to select the number of the character to be re-programmed, e.g. POKE ( E014H ),128 selects display code 128 to be altered.

E015 is used to select the line of the character to be re-programmed, e.g. POKE ( E015H ),0 selects the top line of character 128 to be altered, whilst POKE ( E015H ),7 selects the bottom line.

Once E014 and E015 have been set up the user must POKE ( E016H ),X to actually re-program the Chr. Each pixel is one bit of the byte X with the MSB displayed on the left of the line.

e.g. POKE ( E016H ),10101000 =
Program to program a chr below. Say we want display code character number 128 to look like this

10 POKE (E014H), 128 : REM SELECT CHR 128
20 FOR A = 0 TO 7 : POKE (E015H), A : REM SELECT LINE NO.
30 READ B : POKE (E016H), A : REM PROGRAM LINE
40 NEXT A : END : REM DO NEXT LINE
50 DATA 153, 90, 60, 24, 24, 60, 90, 153

The circuit is built on Vero V-Q Board using the Vero wire system. The board is mounted similarly to the Quantum board on the MZ80K. Both the C-ROM and the CPU go on the vero, plugged into wire wrap sockets which are arranged on the vero so that the wire wrap sockets plug straight into the main PCB. The prize question is:- how do you do this on the MZ80A PCB?

The circuit diagram appeared in the last magazine. It must be emphasised that this board, although quite effective for high resolution diagrams on the screen, will shortly be replaced by a more advanced board. It is nevertheless an interesting project for home constructors and with a little ingenuity could be fitted to the MZ80A computer. Programming instructions were also given in the last magazine.

Wiring Details

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5v Rail

		
pin 11 Z80 to pin 14 IC8 to pin 14 IC9 to pin 16 IC10 to pin 20 IC1 to 
pin 20 IC2 to pin 20 IC3 to pin 19 IC4 to pin 24 IC4 to pin 1 IC5 to
pin 20 IC5 to pin 20 IC6 to pin 20 IC7 to pin 24 CGROM.

0v Rail

pin 29 Z80 to pin 7 IC8 to pin 7 IC9 to pin 8 IC10 to pin 1 IC1 to pin 
10 IC1 to pin 10 IC2 to pin 10 IC3 to pin 12 IC4 to pin 18 IC4 to pin 
20 IC4 to pin 10 IC5 to pin 1 IC6 to pin 10 IC6 to pin 1 IC7 to pin 10
IC7 to pin 12 CGROM.

various

		
pin 30 Z80 to pin 15 IC10
pin 31 Z80 to pin 14 IC10
pin 13 IC10 to pin 12 IC10 to pin 6 IC30 on main PCB
pin 3 IC10 to pin 3 IC8 to pin 19 IC1 to pin 1 IC2 to pin 1 IC3 to pin 1 IC9
pin 4 IC8 to pin 19 IC6 to pin 19 IC7
pin 2 IC10 to pin 5 IC8
pin 1 IC10 to pin 9 IC8
pin 6 IC8 to pin 11 IC3
pin 8 IC8 to pin 11 IC2
pin 22 Z80 to pin 2 IC9
pin 14 Z80 to pin 18 IC1 to pin 3 IC2 to pin 3 IC3
pin 15 Z80 to pin 17 IC1 to pin 4 IC2 to pin 4 IC3
pin 12 Z80 to pin 16 IC1 to pin 7 IC2 to pin 7 IC3
pin 8 Z80 to pin 15 IC1 to pin 8 IC2
pin 7 Z80 to pin 14 IC1 to pin 18 IC2
pin 9 Z80 to pin 13 IC1 to pin 17 IC2
pin 10 Z80 to pin 12 IC1 to pin 14 IC2
pin 13 Z80 to pin 11 IC1
pin 3 IC9 to pin 21 IC4
pin 2 IC3 to pin 8 IC4 to pin 2 IC7
pin 5 IC3 to pin 7 IC4 to pin 3 IC7
pin 6 IC3 to pin 6 IC4 to pin 4 IC7
pin 18 IC7 to pin 8 CGROM
pin 4 IC1 to pin 11 IC4 to pin 16 IC5
pin 17 IC7 to pin 7 CGROM
Pin 5 IC1 to pin 13 IC4 to pin 15 IC5
pin 16 IC7 to pin 6 CGROM
pin 6 IC1 to pin 14 IC4 to pin 14 IC5
pin 2 IC2 to pin 5 IC4 to pin 2 IC6
pin 7 IC1 to pin 15 IC4 to pin 13 IC5
pin 5 IC2 to pin 4 IC4 to pin 3 IC6
pin 8 IC1 to pin 16 IC4 to pin 12 IC5
pin 6 IC2 to pin 3 IC4 to pin 4 IC6
pin 9 IC1 to pin 17 IC4 to pin 11 IC5
pin 9 IC2 to pin 2 IC4 to pin 5 IC6
pin 2 IC5 to pin 9 CGROM
pin 19 IC2 to pin 1 IC4 to pin 6 IC6
pin 3 IC5 to pin 10 CGROM
pin 16 IC2 to pin 23 IC4 to pin 7 IC6
pin 4 IC5 to pin 11 CGROM
pin 15 IC2 to pin 22 IC4 to pin 8 IC6
pin 5 IC5 to pin 13 CGROM
pin 18 IC6 to pin 5 CGROM
pin 6 IC5 to pin 14 CGROM
pin 17 IC6 to pin 4 CGROM
pin 7 IC5 to pin 15 CGROM
pin 16 IC6 to pin 3 CGROM
pin 8 IC5 to pin 16 CGROM
pin 15 IC6 to pin 2 CGROM
pin 9 IC5 to pin 17 CGROM
pin 14 IC6 to pin 1 CGROM
pin 1 IC8 to pin 20 CGROM to centre poll of switch
pin 13 IC6 to pin 23 CGROM
end 1 of switch to pin 24 CGROM
pin 12 IC6 to pin 22 CGROM
end 2 of switch to pin 19 CGROM
pin 19 IC5 to pin 2 IC8
pin 2 IC1  to pin 9 IC4 to pin 18 IC5
pin 3 IC1 to pin 10 IC4 to pin 17 IC5