LB-Z80-01

Features

• Z80 CPU
• Oscillator 8 MHz nominal on card
• Reset switch/power monitor
• Address decoder PLD drives RAM/ROM/IO chip selects
• 100x50mm card

Memory Map

• 0x0000-0x1FFF 8KB ROM
• 32KB or 56KB SRAM
  • 0x8000-0xFFFF Using LB-MEM-02 has 32 KB SRAM
  • 0x2000-0xFFFF Using LB-MEM-04 has 128KB or 512 KB of SRAM so 56 KB can be available
• I/O
  • 0x00-0x7F - Free
  • 0x80-0x81 - Serial port (ACIA)

Design

CPU and Power Supervisor/Reset

• Z80 CPU
• Oscillator 8 MHz nominal on card
• Reset switch/power monitor

Z80 Register Set

Memory Access Timing

I/O Access Timing

Oscillator

• 8MHZ or 10 MHz oscillator

PLD

• ATF16V8B part
• TL866ii Plus Programmer

PLD Listing

Name       LB-Z80-01_PLD;
Partno     ATF16V8B;
Date       10/14/24;
Revision   02;
Designer   DOUG G;
Company    LAND BOARDS LLC;
Assembly   LB-Z80-01_U2;
Location   Rustbelt, US;
Device     G16V8;

/* Rev 2 PCB
*/


/* Control inputs */
PIN    1   = CLK;
PIN    2   = CPUA13;
PIN    3   = CPUA14;
PIN    4   = CPUA15;
PIN    5   = !MREQ;
PIN    6   = !IORQ;
PIN    7   = !M1;
PIN    8   = !CPURD;
PIN    9   = !CPUWR;
PIN    11  = CPUD0;

/* Address Decode and Chip Select outputs */
PIN    13  = !ROMCS;
PIN    14  = !IOCS;
PIN    15  = !RAMCS;
PIN    16  = !MEMRD;
/* PIN    17  = !WAIT; */
PIN    18  = LED;

ROMCS = !CPUA15 & !CPUA14 & !CPUA13 & MREQ & CPURD;

/* 56KB SRAM */
/*
RAMCS = CPUA15 & MREQ
#       CPUA14 & MREQ
#       CPUA13 & MREQ;
*/

/* 32KB SRAM */
RAMCS = CPUA15 & MREQ;

IOCS = !M1 & IORQ;

/*
WAIT = !MREQ # !IORQ;
*/

MEMRD = CPURD;

LED =     !CPUA15 & !CPUA14 & !CPUA13 & MREQ & CPUWR & CPUD0
# LED & !(!CPUA15 & !CPUA14 & !CPUA13 & MREQ & CPUWR);

Backplane Connector

Software

Assembly Language Toolchain

• TASM.EXE - Telemark Assembler
  • The Telemark Assembler (TASM) User's Manual
  • 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 TASM80.TAB to run on Win 11

ACIA Loopback Test Code

• AciaTest.asm - Source code
• Type a character, get it back
  • 115,200 baud, 1 stop bit, no parity
• Works

String Test Code

• StringTest.asm - Source code
• String write code
• Includes loopback code
• Works

String Read/Interpreter Code

• ReadStringTest.asm - Source code
• Adds a string read function
• Adds an interpreter skeleton
• Works with Rev 1 card
• Added LED command (Rev 2 card)
  • L0 - Turn off the LED
  • L1 - Turn on the LED
• Works with Rev 2 card

NASCOM 2 BASIC

• Microsoft BASIC 4.7 modified to remove all hardware-specific code
  • Use Grant Searle's 32KB SRAM version if the LB-MEM-02 card is used
  • Use Grant's 56KB version if the LB-MEM-03 card is used
• Needed to make some minor changes to get the code to run
• Code Repo
• Works

Short Test Program

10 I=0
20 PRINTI:I=I+1:GOTO 20

Build Details

• TASM assembler (see above)
• S Record and Hex file manipulation
  • Examples of srec_cat utility
  • srec_cat man page
• Adds srec_cat to combine files into one Intel Hex file
  • 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

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

• List files
  • INTMINI.LST
  • BASIC.LST
• Hex files
  • INTMINI.HEX
  • BASIC.HEX
  • ROM32.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).
• Hex file format

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

Software Development Tools

• SDCC - Small Device C Compiler
  • SDCC Compiler User Guide

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-
• ASCII Table

Mechanicals

Rev 2 Mechanicals

Rev 1 Mechanicals

Checkout

Rev 2 Checkout

• Reset switch footprint is good
• LED control worked with software update
  • Write 1 to address in range 0x0000-0x1FFF to turn LED on (command L1)
  • Write 0 to address in range 0x0000-0x1FFF to turn LED off (command L0)
• Serial test software runs
• MS BASIC doesn't work

Rev 2 Changes

• Fixed resistor silkscreen values
• Re-sequenced resistor reference designator
• Made reset switch right angle
• Add LED and resistor to PLD pin 15
• Add CPUD0 to PLD pin 11
• Added bulk capacitor

Rev 1 Checkout

• Didn't use silkscreen values, used
  • R1 = 4.7K
  • Other resistors are 10K
• Z80 nop tester nop = 0x00
  • Refresh complicates this
• Made C2 a bulk cap (100uF)

Assembly Sheet

• Interactive BOM