SIMPLE-68008

Features

• 68008 CPU
  • 20 bit address space (1MB total)
• 10 MHz clock
• 128KB/512KB SRAM
• Up to 448KB EPROM/EEPROM
• 68681 Dual Serial Port (ACIA)
  • Headers for FTDI
  • 38,400 baud
• Reset switch with optional Power Supervisor
• 5V operation
  • 375 mA nominal
• 95x95mm card
• (4) 6-32 mounting holes

Memory Map

• The memory map depends on two things
  • Mapping in the PLDs
  • The firmware that is being run on the card

Maximal Capacity Design

• 0x00000-0x7FFFF 512KB SRAM
• 0x80000-0xEFFFF Up to 448KB EPROM (minus DUART I/O space)
• 0x80000-0x87FFF 27C256 (322KB)
• 0x80000-0x8FFFF 27C512 (64KB)
• 0xF0000-0xFFFFF Serial (ACIA)

Chip Set

• On Ebay
  • $20 plus $9 shipping (2024-08)

Parts in "Kit"

• MC68000P10 - 68K CPU with 16-bit data bus and 24-bit address bus
• MC68230P8 - Parallel I/O bits, timer
• TMP68681P - Dual UART, 8-bit I/O, 6-bit I/O
• MC68901P - Multifunction (8 I/O pins, interrupt controller, (4) timers, UART
• AM8511A - Floating Point Unit
• MC68008P10 - 68K CPU with 8-bit data bus and 20-bit address bus
• 65B50P - ACIA (Serial interface)

Design

CPU

• The Motorola 68008 is an 8/32-bit microprocessor introduced by Motorola in 1982
  • It is a version of 1979's Motorola 68000 with an 8-bit external data bus, as well as a smaller address bus
  • This card uses a 68008 with 20 address lines (48-pin package) which allowed 1 MB address space versus the 16 MB addressable on the 68000
• Rev 1 needs a wire jumper U5-39 to U5-40 to pull up VPA*

CPU Timing

Function Code

EPROM

• SST27C256 EEPROM
  • 32 KB part
  • 28 pin part, 32 pin socket

Flash Memory (EEPROM) Programming

• Program using TL-866ii plus programmer
• Select device type
  • Using SST 27SF256 part (Part is 32 KB)
• File Open
• Select file = S68K_001.hex
• File format: INTEL_HEX
• To Region: Default
• Set EPROM offset when file is loaded to accommodate memory map offsets for EPROM space
  • Set From File Start Addr(Hex) to 80000
  • To Buffer Start Addr(Hex) to 00000 (should be already that value)

• Got Device ID error
  • Turn off ID checkbox in the Options section (bottom left of window)
• Device programmed/verified
• Memory Buffer should look like

Device ID Mysteries

• Ebay has parts with SST marking
• EPROM Programmer says the parts are WinBond (Manufacturer ID 0xDA)
  • Manufacturers ID list
• Part marked as 27SF512 and it's a 27C512 (Part ID 0x08)
• Windbond 27C512 qty 10 are cheaper than SST part on ebay

SRAM

• Using 512 KB SRAM
  • Wire jumper H6-2 to H6-3 on rear of card

Dual UART

Reset

Clock

• Test and works with 8 MHZ and 10 MHz crystal oscillator

PLDs

• Two ATF16V8B PLDs (Datasheet)
• WinCupl compiler
  • WinCupl Download link
• Program using TL-866ii plus programmer

PLD_001

PLD_001 Source Listing

• Source file
• JEDEC Programming file
• WAIT1 and WAIT2 are not used since the DUART has a DTACK* out and the EPROM/SRAM run at zero wait states

Name       SIMPLE-68008_PLD_1;
Partno     ATF16V8B;
Date       07/13/24;
Revision   01;
Designer   DOUG G;
Company    LAND BOARDS LLC;
Assembly   U02;
Location   RUSTBELT, USA;
Device     G16V8;

/*
*/

/* Inputs */
PIN    1   = CLK;
PIN    2   = !CPUAS;
PIN    3   = !CPUDS;
PIN    4   = CPUA16;
PIN    5   = CPUA17;
PIN    6   = CPUA18;
PIN    7   = CPUA19;
PIN    8   = CPUFC0;
PIN    9   = CPUFC1;
PIN    11  = CPUFC2;
PIN    12  = !DDTACK;
PIN    13  = SWAP;

/* Outputs */
PIN    14  = !CPUIACK;
PIN    15  = !DUARTCS;
PIN    16  = !CPUDTACK;
PIN    17  = WAIT1;
PIN    18  = !RAMSEL;
PIN    19  = WAIT2;

CPUIACK = CPUA19 & CPUA18 & CPUA17 & CPUA16 & CPUFC2 & CPUFC1 & CPUFC0 & CPUDS;

DUARTCS = CPUA19 & CPUA18 & CPUA17 & CPUA16 & CPUDS & !CPUFC1 &  CPUFC0;

RAMSEL = !CPUA19 & SWAP & CPUDS & !CPUFC1 &  CPUFC0  		/* User/Super Data */
#        !CPUA19 & SWAP & CPUDS &  CPUFC1 & !CPUFC0; 		/* User/Super Program */

CPUDTACK = CPUA19 & CPUA18 & CPUA17 & CPUA16 & CPUDS & !CPUFC1 & CPUFC0 & DDTACK		/* DUART Data spaces	*/
#	    CPUA19 & CPUA18 & CPUA17 & CPUA16 & CPUDS & CPUFC2 & CPUFC1 & CPUFC0 & DDTACK	/* DUART IACK space */
#          CPUA19 & !CPUA18 & CPUDS								/* EPROM	*/
#          CPUA19 & !CPUA17 & CPUDS								/* EPROM	*/
#          CPUA19 & !CPUA16 & CPUDS								/* EPROM	*/
#          !CPUA19 & CPUDS;									/* RAM 		*/

PLD_002

• The SWAP line maps the EPROM to the SRAM space
  • Used to pull the Stack pointer and start address from EPROM
  • Set to 0 at power up
  • Clear early in the startup code to allow SRAM to be used

PLD_002 Source Listing

• Source file
• JEDEC Programming file

Name       SIMPLE-68008_PLD_2;
Partno     ATF16V8B;
Date       06/19/24;
Revision   01;
Designer   DOUG G;
Company    LAND BOARDS LLC;
Assembly   U03;
Location   RUSTBELT, USA;
Device     G16V8;

/*
	RESET CONTROLLER, ROM CHIP SELECT
*/

/* Inputs */
PIN    1   = CLK;
PIN    2   = !CPUWR;
PIN    3   = !CPUDS;
PIN    4   = CPUA16;
PIN    5   = CPUA17;
PIN    6   = CPUA18;
PIN    7   = CPUA19;
PIN    8   = !POR;
PIN    9   = CPUD0;

/* Outputs */
PIN	  13  = SWAPADR;
PIN    14  = SWAP;
PIN    15  = !ROMCS;
PIN    16  = !MEMRD;
PIN    18  = !CPUHLT;
PIN    19  = !CPURES;

/* CLEAR SWAP AT POWER UP, RESET	*/
/* SET SWAP BY 1ST WR TO START OF EPROM SPACE		*/
/* SWAP.CK = CLK; */
/* SWAP.AR = POR; */

MEMRD = !CPUWR & CPUDS & !CPUA19
#       !CPUWR & CPUDS &  CPUA19 & !CPUA18
#       !CPUWR & CPUDS &  CPUA19 & !CPUA17
#       !CPUWR & CPUDS &  CPUA19 & !CPUA16;

SWAP = CPUDS &  CPUWR & CPUA19 & !CPUA18 & !CPUA17 & !CPUA16 & CPUD0 & !POR
#      SWAP  & !POR;

SWAPADR = CPUDS & CPUWR & CPUA19 & !CPUA18 & !CPUA17 & !CPUA16;

ROMCS = CPUDS & !CPUWR & CPUA19 & !CPUA18
#       CPUDS & !CPUWR & CPUA19 & !CPUA17
#       CPUDS & !CPUWR & CPUA19 & !CPUA16
#       CPUDS & !CPUA19 & !CPUA18 & !CPUA17 & !CPUA16 & !SWAP;

CPUHLT.OE = POR;
CPUHLT = POR;

CPURES.OE = POR;
CPURES = POR;

Headers / Connectors

J1 - 2 port FTDI / TTL Serial

• 2x6 header
• Direct connect to DTE RS-232 card
• Flip order to connect to USB to TTL Serial (FTDI)
  • TX<>RX
  • RTS<>CTS
• Pinout

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

J2 - Input Port

1. Input 2
2. Input 5
3. Input 4
4. Input 3
5. Vcc
6. GND

J3 - Output Port

1. GND
2. Vcc
3. Output 7
4. Output 6
5. Output 5
6. Output 4
7. Output 3
8. Output 2

H1 - 5V Power

• 2x4 header

H2-H5 - EPROM/EEPROM Select Jumpers

• H2 = EE PIN 31
• H3 = EE PIN 3
• H4 = EE PIN 30
• H5 = EE PIN 29

27SF256

• 27SF256 is a 28 pin part, socket is 32 pins
  • H2 = Not installed
  • H3-2 to H3-3 = A15 (Vpp on 27SF256, but pin can be either high or low)
  • H4-1 to H4-2 = Vcc
  • H5-2 to H5-3 = CPUA14

EEPROM Jumpers

27040	27020	27010	27512	27256	27128	2764	PIN(32)	PIN(28)		PIN(28)	PIN(32)	2764	27128	27256	27512	27010	27020	27040
VPP	VPP	VPP	N/A	N/A	N/A	N/A	1	N/A		N/A	32	N/A	N/A	N/A	N/A	VCC	VCC	VCC
A16	A16	A16	N/A	N/A	N/A	N/A	2	N/A		N/A	31 (H2)	N/A	N/A	N/A	N/A	PGM	PGM	A18
A15	A15	A15	A15	VPP	VPP	VPP	3 (H3)	1		28	30 (H4)	VCC	VCC	VCC	VCC	N/C	A17	A17
A12	A12	A12	A12	A12	A12	A12	4	2		27	29 (H5)	PGM	PGM	A14	A14	A14	A14	A14
A7	A7	A7	A7	A7	A7	A7	5	3		26	28	A13	A13	A13	A13	A13	A13	A13
A6	A6	A6	A6	A6	A6	A6	6	4		25	27	A8	A8	A8	A8	A8	A8	A8
A5	A5	A5	A5	A5	A5	A5	7	5		24	26	A9	A9	A9	A9	A9	A9	A9
A4	A4	A4	A4	A4	A4	A4	8	6		23	25	A11	A11	A11	A11	A11	A11	A11
A3	A3	A3	A3	A3	A3	A3	9	7		22	24	OE*	OE*	OE*	OE*	OE*	OE*	OE*
A2	A2	A2	A2	A2	A2	A2	10	8		21	23	A10	A10	A10	A10	A10	A10	A10
A1	A1	A1	A1	A1	A1	A1	11	9		20	22	CE*	CE*	CE*	CE*	CE*	CE*	CE*
A0	A0	A0	A0	A0	A0	A0	12	10		19	21	D7	D7	D7	D7	D7	D7	D7
D0	D0	D0	D0	D0	D0	D0	13	11		18	20	D6	D6	D6	D6	D6	D6	D6
D1	D1	D1	D1	D1	D1	D1	14	12		17	19	D5	D5	D5	D5	D5	D5	D5
D2	D2	D2	D2	D2	D2	D2	15	13		16	18	D4	D4	D4	D4	D4	D4	D4
GND	GND	GND	GND	GND	GND	GND	16	14		15	17	D3	D3	D3	D3	D3	D3	D3

H6 - SRAM Configuration

• 1-2 = 128KB SRAM
• 2-3 = 512KB SRAM
• 128KB and 512KB Parts are about the same price so there's not much point (if buying parts anyway) with going with 512KB part
  • AS6C4008-55PCN is $6.38 (2024-06)
  • AS6C1008-55PCN is $2.91 (2024-06)

SIMPLE-68008 Software

• SIMPLE-68008 Code Repository
• 68000 code development is done with cross assemblers/compilers using GCC tools under Linux
• 68000 Assembly Language YouTube Playlist

Linux Development Environment

• Using Oracle VM VirtualBox
• Running Linux Mint
• The GNU C-Compiler with Binutils and other useful tools for 68000 cross development
• This is a Makefile based approach to build the toolchain to reduce the build time.
• The original work was by Steve Moody's page
• These tools are build:
  • binutils
  • gcc with libs for C/C++/ObjC
  • vasm
  • vbcc
  • vlink
  • newlib

S Record and Hex file manipulation

• Examples of srec_cat utility
• srec_cat man page

Initial Test Code

• S68K_001 - Test Code Repo
• Uses m68k assembly code toolchain
• Set up stack, starting address
• 68681 DUART code
  • 9600 baud
  • Initialize DUART
  • Input/Output Serial routines
• Loop forever

68k-Monitor

• S68K_002 - Monitor Code Repo here
• Uses m68k assembly code toolchain
• Built from ChartreusK 68K monitor = 68901 DUART code
• Added S-Record load ('L' on command line)
  • S record format
• Runs at 38,400 baud with no waits/handshakes on transmit from Host Side
• Added improved SRAM test code
• Added SRAM fill
• Added 60 Hz timer code
• Type 'T' to start timer
  • Long word timer at 0x608-0x60b
  • Can be used as random number value if code is run from SRAM since the lowest byte s/b continually updated

Example Assembly Code

• S68K_003 - Assembly Code Example Repo
  • 68000 Assembly Programming
• Uses m68k assembly code toolchain
• Runs out of SRAM
• Loops forever
• Blinks LED connected to O2 (red LED, 4.7K resistor, wired to ground)
• Load and run

SIMPLE-68008 CPU
RAM Test Passed
> L
Load S-Record
+++++>
> R1000

Example C Code

• S68K_004 - C Code Example Repo
• Uses m68k assembly code toolchain
• Runs out of SRAM
• Loops forever
• Blinks LED connected to O2 (red LED, 4.7K resistor, wired to ground)
• Load and run

SIMPLE-68008 CPU
RAM Test Passed
> L
Load S-Record
+++++>
> R2000

String Test C Code

• S68K_005 - C Code Example Repo
• Uses m68k assembly code toolchain
• ASCII code
• Runs out of SRAM
• Loops forever
• Blinks LED connected to O2 (red LED, 4.7K resistor, wired to ground)
• Load and run

SIMPLE-68008 CPU
RAM Test Passed
> L
Load S-Record
+++++>
> R2000

Test Transmit Interrupt Code

• S68K_006 - Interrupt Test Code Example Repo
• Uses m68k assembly code toolchain
• Runs out of SRAM
• Loops forever
• Sends out alphabet forever using Transmit interrupt from 68681
• Required jumper U5-39 to U5-40 to always pullup VPA* to Vcc

SIMPLE-68008 CPU V1.00
RAM Test Passed
> l
Load S-Record
++++++++++++++++++++>
> r1000
SIMPLE-68008 CPU V1.00
RAM Test Passed
> r1100
42345678S:;<I>?@ABMDPFGHLJKE-6O8QRS00VW8 Z[\C^_`PbUd fghijkVm1o.qrst0vwx0z2
]R7AM:; =>T@ABeDEsGt JKLPNaPsRSsUVWXed[ >` bcdefghijklmnopqrstuvwxyz
23456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz
23456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz
23456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz
23456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz
23456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz

Receive Interrupt Test Code

• S68K_007 GitHub Repository
• Test interrupt from DUART
  • Using receive character interrupt
• Runs from RAM
• Echos back character typed
• Downloaded as S Records
  • Loaded with L command in S68K_002 monitor
• R1000 to run program

60 Hz timer

• S68K_008 GitHub Repository
• Make a 60 Hz Counter in memory
• Use timer in DUART
• 3.6864 MHz / 16 = 23400
• 23,400 / 60 (Hz) / 2 per cycle = 1920 count = 0x780
• Increment a long in 0x604(-0x607)
• 60 Hz is 0x780 divisor
• Stop timer to clear timer
• Restart timer to set up interrupt on next timer edge

Guess a Number Game Code

• S68K_GAME_01
  • Game to guess a number from 1-99
    • Missing random number generator
  • Structures string and DUART I/O code into separate files
• S68K_GAME_02
  • Game to guess a number from 1-99
    • Version adds random number generator
  • Slightly less clumsy includes (added a main() stub and moved includes to right after that)

Sample Game with ANSI screen control

• S68K_GAME_03
• Move an object around the screen using arrow keys
• To load it into the S68K_002 monitor you can run the command "L" and then send the run (S record) .run file to the serial port
• Run the program from the S68K_002 monitor using R2000
  • Output should look like the following:

SIMPLE-68008 CPU

RAM Test Passed

 > l

Load S-Record

++++++++++++++++++++++++++++>

 > r2000

• Scrren should clear and a '*' will be at the center
• Arrow keys to move around the '*'
• Q to quit

ANSI Terminal Driver

• nncurses
  • Similar to ncurses
    • nncurses is not ncurses
      • n curses is not curses
• Drive ANSI/VT terminal
  • Terminal apps under Linux/Windows putty or Tera Term
• Double buffered implementation
  • Write to fromBuffer[][]
  • Copy to screenBuffer[][]
  • Send out delta as ANSI sequences to the Serial Terminal
• ASCII code table
• ANSI.SYS
• ANSI/VY-xxx ESC sequences

Sample Game

• S68K_GAME_04
• Game framework with basic game elements
• Written in C
• Writes to ANSI screen
  • Uses cursor position commands
• Draws border on the screen
• Status line at the bottom of the screen
• Puts '*' at center of the screen
• Arrow keys move '*' around the playfield

First Person Shooter Game

• S68K_GAME_06
• Runs on ANSI/VT terminal
• First person shooter
• Scores of hits/misses
• Elapsed time since game start
• Target random movement based on modulo of timer

Enhanced BASIC (Running from SRAM)

• Lee Davidson's Enhanced BASIC
  • Enhanced 68k BASIC by Lee Davison
  • BASIC Commands
  • 68K example code
• 38,400 baud serial connection (monitor and BASIC)
• Running BASIC from card reset

SIMPLE-68008 CPU
RAM Test Passed

• L for Load

> l
Load S-Record
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++>

• Run at 800

> R800
457232 Bytes free

Enhanced 68k BASIC Version 3.52

Ready

• Test with short program

10 PRINT "HI"
RUN
HI

Ready

68K Monitor Plus Enhanced BASIC (Running from ROM)

• Puts S68K_002 - Monitor Code and Enhanced BASIC into a single 32KB ROM
• Build steps
  • Run make for S68K_002
• Run make for the Enhanced BASIC which pulls in the S68K_002 code
  • Result is a .hex file
• EPROM base address = 0x80000
  • 0x80000-0x83FFF - First 16KB reserved addresses for monitor (plenty of room for expansion)
    • Code is from 0x80400-0x80caf (Less than 4KB)
  • 0x84000-0x87FFF - Second 16KB reserves addresses for BASIC (plenty of room for expansion)
    • Code is from 0x84800-0x87D1F (Less than 16KB)
• Boots into the monitor
• Run BASIC with 'B' on command line
• Runs at 38,400 baud

SIMPLE-68008 CPU V1.00
RAM Test Passed
> b
12
490032 Bytes free

Enhanced 68k BASIC Version 3.52

Ready

68000 fig-FORTH V1.0

• Source Repository
• Runs from SRAM
• Run at 3648
• From reset

SIMPLE-68008 CPU V1.00
RAM Test Passed
> l
Load S-Record
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++>
> r3648

68000 fig-FORTH V1.0
    OK
    OK
    OK
1 2 3     OK
+    OK
+    OK
. 6    OK

Mechanicals

• Rev 1 card

Checkout

Rev 2 Card

• Fixed DUART TXB and RXA connections (see Rev 1 rework)
• Added pullup to VPA* line (to make interrupts work - see Rev 1 rework)
• Add some silkscreen annotations for memory configuration header connections to rear of card
• Moved R6 up and added more silkscreen near CPU
• Added R7 resistor and LED to ground on U3-12
  • Access with a write of but D0 to EEPROM address (similar to SWAP bit)

Rev 1 Card

• VPA needs to be pulled up
  • Add wire U5-39 to U5-40
• Reset working
  • Reset switch and monitor working
• Clock working
  • Checked at 8 and 10 MHz
• EPROM working
• SRAM working
• Checked Serial port
  • Not using any XTAL capacitors
• Serial transmit/receive lines swapped
  • TXB and RXA are swapped on DUART
  • U6 pins 11 and 31 need to be swapped

• Easiest cuts (on bottom of board)

• Cuts as seen from the top side Silkscreen

• 2 Jumpers

• Alternative cut (harder due to space and being on top of board)

Assembly Sheet

Rev 1

• SIMPLE-68008 Rev 1 Assembly Sheet
• SIMPLE-68008 Rev 1 Interactive BOM