SIMPLE-Z80

Features

• Build of Grant Searles's Simple Z80 CPU
  • Runs BASIC
• Z80 CPU
• 7.3728 MHz clock
• 56KB SRAM (uses 128KB parts)
• 8KB EPROM/EEPROM
• 68B50 Serial Port (ACIA)
  • RS-232 port
  • Header for FTDI
  • 115,200 baud
• Reset switch with optional DS1813 Power Supervisor
• 95x95mm card
• (4) 6-32 mounting holes

Memory Map

• 0x0000-0x1FFF 8KB ROM
• 0x2000-0xFFFF 56KB SRAM
• I/O
  • 0x00-0x7F - Free
  • 0x80-0x81 - Serial port (ACIA)

Chip Set

• Ebay listing
  • Needs 68B50 to run Grant's code

Design

• CPU

• EPROM

• SRAM

• ACIA

• Clock

Headers / Connectors

J1 - RS-232 Serial

• DB-9 Male
• Pinout

1. N/C
2. Receive
3. Transmit
4. Loop to pin 6
5. GND
6. Loop to pin 4
7. RTS
8. N/C
9. N/C

J2/J5 - EPROM/EEPROM Select Jumpers

EEPROM Pin Table

27512	27256	27SF256	28C256	27128	2764	28C64	PIN		PIN	2764	28C64	27128	28C256	27SF256	27256	27512
A15	VPP	VPP	A14	VPP	VPP	N/C	1		28	VCC	VCC	VCC	VCC	VCC	VCC	VCC
A12	A12	A12	A12	A12	A12	A12	2		27	PGM	WE*	PGM	WE*	A14	A14	A14
A7	A7	A7	A7	A7	A7	A7	3		26	A13	N/C	A13	A13	A13	A13	A13
A6	A6	A6	A6	A6	A6	A6	4		25	A8	A8	A8	A8	A8	A8	A8
A5	A5	A5	A5	A5	A5	A5	5		24	A9	A9	A9	A9	A9	A9	A9
A4	A4	A4	A4	A4	A4	A4	6		23	A11	A11	A11	A11	A11	A11	A11
A3	A3	A3	A3	A3	A3	A3	7		22	OE*	OE*	OE*	OE*	OE*	OE*	OE*
A2	A2	A2	A2	A2	A2	A2	8		21	A10	A10	A10	A10	A10	A10	A10
A1	A1	A1	A1	A1	A1	A1	9		20	CE*	CE*	CE*	CE*	CE*	CE*	CE*
A0	A0	A0	A0	A0	A0	A0	10		19	D7	D7	D7	D7	D7	D7	D7
D0	D0	D0	D0	D0	D0	D0	11		18	D6	D6	D6	D6	D6	D6	D6
D1	D1	D1	D1	D1	D1	D1	12		17	D5	D5	D5	D5	D5	D5	D5
D2	D2	D2	D2	D2	D2	D2	13		16	D4	D4	D4	D4	D4	D4	D4
GND	GND	GND	GND	GND	GND	GND	14		15	D3	D3	D3	D3	D3	D3	D3

J3 - FTDI / TTL Serial

1. GND
2. N/C
3. +5V
4. Transmit (out)
5. Receive (in)
6. RTS* (out)

J4 - 5V Power

• 2x4 header

Software

• ROM.HEX - ROM file
• Nascom Computer BASIC modified to remove all hardware-specific code

Source files

• intmini.asm - the interupt driven mini startup program needed to boot into BASIC
• basic.asm - BASIC 4.7b - a conversion of Microsoft BASIC 4.7, as used on the Nascom computers (see below for details)

Output files

• INTMINI.HEX
• BASIC.HEX
• ROM.HEX - the complete 8K ROM ready for burning to an EPROM - the unused contents are filled with FF values.
• Within the ROM, the serial handler is first (starting at address 0000H), followed by the BASIC interpreter (starting at 0100H).

Assembler files (for Windows/DOS)

• _ASSEMBLE.BAT - double-click in Windows to run the assembly if needed
• TASM.EXE
• TASM80.TAB

Acknowledgements

• BASIC is Microsoft BASIC 4.7 for the NASCOM, heavily modified by Grant to remove references to different monitors, screen handlers and keyboard matrix reading
• TASM assembler is a partial distribution of the package from Speech Technology Incorporated

Mechanicals

SIMPLE-Z80 Assembly Sheet

• SIMPLE-Z80 Rev 1 Assembly Sheet
• SIMPLE-Z80 Rev 1 Interactive BOM