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

• Requires a FTDI cross-over cable

• Pinout

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

J4 - 5V Power

• 2x4 header

First Unit Checkout

• PCB

Install Sockets

• Machined pin sockets

Power

• Install 2x4 at J4
• Power card via J4 with 5V
• Check power pins on parts

Clock

• Install Clock parts
  • Install R2, R3
  • Install C5, C6
  • Install 7.3728 MHz crystal
  • Install 74HC04 at U5
• Measure clock at U5-4
  • 7.32 MHz clock - looks good

Reset

• Do not install U8 Power Monitor
  • Reset button gets stretched by Power Monitor U9
• Install pushbutton switch SW1
• Measure reset at Z80 U2 pin marked RST on silkscreen

EPROM

• U6 = SST27C256 EEPROM
  • 32 KB part
  • Using first 16KB of EEPROM
  • J2 EEPROM pin 1 = VPP = VCC or GND
    • Jumper J2:2-3
  • J5 EEPROM pin 27 = A14 = GND
    • Jumper J5:2-3

EEPROM Programming

• Program using TL-866ii plus programmer
• File = ROM.HEX - I/O routines plus BASIC
• Got Device ID error
• Turn off ID check

• Device programmed/verified

Install CPU, ROM, RAM, ACIA

• U1 - Do not install MAX232 yet
  • Use FTDI connector with FTDI-49MM card

Test FTDI Serial

• Wiring is not 1:1 to FTDI-49MM
• Wire FTDI J3 to FTDI-49MM card
  • FTDI-49MM GND pin 1 to J3-1 RX on card
  • FTDI-49MM VCC pin 3 to J3-3 RX on card
  • FTDI-49MM TX pin 4 on to J3-5 RX on card
  • FTDI-49MM RX pin 5 on to J3-4 TX on card
  • FTDI-49MM CTS(in) pin 2 to J3-6 CTS on card

Test RS-232 Serial

• With MAX232
• Install DB-9 Male
• Holes don't line up well, but 4-40 screws can fit
• Connected to FTDI-49MM and DCE cards
  • FTDI-49MM and DCE cards wired together
  • DCE has female DB-9
  • Separate power cable J2 on FTDI-49MM to J3 on card

• Works

Software

• ROM.HEX - ROM file
• Nascom 2 Computer BASIC Microsoft BASIC 4.7 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

Performance

• TeraTerm settings

• Test software

10 FOR I =1 TO 10000
20 PRINT I
30 NEXT I

• Time ~ secs

Mechanicals

SIMPLE-Z80 Assembly Sheet

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