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

• TL866ii Plus Programmer

SRAM

ACIA

• Requires a FTDI cross-over cable
• Can only use RS-232 or FTDI - one at a time
  • Put MAX232 in a socket if you want flexibility
  • Remove MAX232 if you want to use FTDI

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

• J2 - EPROM Pin 1 jumper
  • 1-2 for 28C64, 28C256 (Pull WE to VCC)
  • 2-3 for 27256, 27SF256, 27512 (Pull A14 to GND)
• J5 - EPROM Pin 27 jumper
  • GND (2-3)

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
• Can only use RS-232 or FTDI - one at a time
  • Put MAX232 in a socket if you want flexibility
  • Remove MAX232 if you want to use FTDI

• 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

Netlist

• First build had six open traces
  • Added wire U2-5 to U4-31
  • Added wire U2-15 to U4-14
  • Added wire U2-20 to U5-5
  • Added wire U2-40 to U4-23
  • Added wire U7-3 to U4-29
  • Added wire U7-11 to U4-30
• Checked on 2 other boards, not an issue on the boards
• Card worked with wires

/CPUA0,U2-30,U3-11,U4-12,U6-10,
/CPUA1,U2-31,U4-11,U6-9,
/CPUA2,U2-32,U4-10,U6-8,
/CPUA3,U2-33,U4-9,U6-7,
/CPUA4,U2-34,U4-8,U6-6,
/CPUA5,U2-35,U4-7,U6-5,
/CPUA6,U2-36,U3-9,U4-6,U6-4,
/CPUA7,U2-37,U3-10,U4-5,U6-3,
/CPUA8,U2-38,U4-27,U6-25,
/CPUA9,U2-39,U4-26,U6-24,
/CPUA10,U2-40,U4-23,U6-21,
/CPUA11,U2-1,U4-25,U6-23,
/CPUA12,U2-2,U4-4,U6-2,
/CPUA13,U2-3,U4-28,U6-26,U7-9,
/CPUA14,U2-4,U4-3,U7-10,
/CPUA15,U2-5,U4-31,U7-13,
/CPUCLK,U2-6,U3-3,U3-4,U5-4,
/CPUD0,U2-14,U3-22,U4-13,U6-11,
/CPUD1,U2-15,U3-21,U4-14,U6-12,
/CPUD2,U2-12,U3-20,U4-15,U6-13,
/CPUD3,U2-8,U3-19,U4-17,U6-15,
/CPUD4,U2-7,U3-18,U4-18,U6-16,
/CPUD5,U2-9,U3-17,U4-19,U6-17,
/CPUD6,U2-10,U3-16,U4-20,U6-18,
/CPUD7,U2-13,U3-15,U4-21,U6-19,
/CPUIORQ*,U2-20,U5-5,
/CPUM1,U2-27,U3-8,
/CPUMREQ*,U2-19,U7-2,U7-4,
/CPURD*,U2-21,U7-5,
/CPUWR*,U2-22,U3-13,U7-1,
/EE_PIN1,J2-2,U6-1,
/EE_PIN27,J5-2,U6-27,
/F-RTS*,J3-6,R5-2,
/F_RX,J3-5,R6-2,
/F_TX,J3-4,R7-2,
/IORQ,U3-14,U5-6,
/IRQ*,R4-2,U2-16,U3-7,
/MEMRD*,U4-24,U6-22,U7-6,
/MEMWR*,U4-29,U7-3,
/ROM0RAM1,U4-30,U6-20,U7-11,
/RS_RTS*,J1-7,U1-14,
/RS_RX,J1-2,U1-8,
/RS_TX,J1-3,U1-7,
/RTS*,R5-1,U1-11,U3-5,
/UART_RX,R6-1,U1-9,U3-2,
/UART_TX,R7-1,U1-10,U3-6,
/~{CPURESB},R1-2,SW1-2,U2-26,U8-1,
GND,C10-1,C11-1,C12-1,C13-1,C14-2,C3-2,C4-1,C5-2,C6-2,C7-1,C8-1,C9-1,J1-5,J2-3,J3-1,J4-1,J4-3,J4-5,J4-7,J5-3,SW1-1,U1-15,U2-29,U3-1,U3-23,U3-24,U4-16,U4-2,U4-22,U5-7,U6-14,U7-7,U8-3,
Net-(C5-Pad1),C5-1,R3-1,Y1-2,
Net-(C6-Pad1),C6-1,R2-1,U5-1,Y1-1,
Net-(J1-Pad4),J1-4,J1-6,
Net-(R2-Pad2),R2-2,R3-2,U5-2,U5-3,
Net-(U1-C1+),C1-1,U1-1,
Net-(U1-C1-),C1-2,U1-3,
Net-(U1-C2+),C2-1,U1-4,
Net-(U1-C2-),C2-2,U1-5,
Net-(U1-VS+),C3-1,U1-2,
Net-(U1-VS-),C4-2,U1-6,
Net-(U7-Pad12),U7-12,U7-8,
VCC,C10-2,C11-2,C12-2,C13-2,C14-1,C7-2,C8-2,C9-2,J2-1,J3-3,J4-2,J4-4,J4-6,J4-8,J5-1,R1-1,R4-1,U1-16,U2-11,U2-17,U2-24,U2-25,U3-12,U4-32,U5-11,U5-13,U5-14,U5-9,U6-28,U7-14,U8-2,

Software

Z80 Register Set

NASCOM 2 BASIC

• Nascom 2 Computer BASIC Microsoft BASIC 4.7 modified to remove all hardware-specific code
  • NASCOM BASIC Source Code - 56KB version
  • NASCOM BASIC Source Code - 32KB version used on LB-Z80-01 card

Toolchain

• TASM.EXE
  • The version of TASM in Grant's build zip file doesn't run under Win 11
  • TASM version that runs on Win 11
• TASM80.TAB
  • [Probably need] the updated one in to run on Win 11
• Assembler files (for Windows 11/DOS)
• S Record and Hex file manipulation
  • Examples of srec_cat utility
  • srec_cat man page
• Combine int32k.hex and BAS32K.HEX into rom32.hex using srec-cat
  • Command line
    • srec_cat.exe int32k.hex -Intel BAS32K.HEX -Intel -fill 0xff 0x0144 0x014f -o rom32.hex -Intel
• _ASSEMBLE.BAT - double-click in Windows to run the assembly if needed
  • Adds srec_cat to combine files into one Intel Hex file

NASCOM BASIC - Code Repository

• NASCOM BASIC Source Code - 32KB version
• NASCOM BASIC Source Code - 56KB version

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).

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

References

• Z80 Assembly Language Programming - Concise description of the register set, Chapter 3 page 1-42 of Z80, assembly language programming by Leventhal, Lance A.
• Programming the Z80 1980 Rodnay Zaks
• Z80, assembly language programming by Leventhal, Lance A., 1945-
• Hex file format

• ASCII Table

Performance

• TeraTerm settings

• Test software

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

• Time ~ 27 secs
• CPU is 4x the clock speed of the SIMPLE-6502 and SIMPLE-6809 cards

Mechanicals

SIMPLE-Z80 Assembly Sheet

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