SIMPLE-6809

Features

• Build of Grant Searles's Simple 6809 CPU
  • Runs BASIC
• 68B09 CPU
• 7.3728 MHz
• 32KB SRAM
• 16KB EPROM/EEPROM
• 68B50 Serial Port (ACIA)
  • RS-232 port
  • Header for FTDI
  • 115,200 baud
• Reset switch with optional Power Supervisor
• 95x95mm card
• (4) 6-32 mounting holes

Memory Map

• 0x0000-0x7FFF 32KB SRAM
• 0x8000-0x9FFF Free Space (8KB)
• 0xA000-0xBFFF Serial (ACIA)
• 0xC000-0xCFFF 16KB EPROM

Chipset

• MC68B09CP
• MC68B50CP
• HM62256BLP-7 32KB SRAM
• SST27SF256-70-3C-PGE EPROM

Design

CPU

CPU Timing

EEPROM

SRAM

Logic ==============

ACIA ==============

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

• Rev 1 PCB silkscreen is wrong (both sides of the card)

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

J4 - 5V Power

• 2x4 header

First Unit Checkout

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 7.3728 MHz crystal
  • Install C5, C6

• Install CPU at U5

Reset

• Install U7 Power Monitor
• Install pushbutton switch SW1
• Reset button gets stretched by Power Monitor U9
• Measure reset at 68B09 U5 pin 37
• Falling edge scope cap

EPROM

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

EEPROM Programming

• Program using TL-866ii plus programmer
• File = ExBasROM.hex
• Set offsets for 27SF256 part
  • Part is 32 KB
  • hex files is 16 KB
• Set From File Start Addr(Hex) to 0C000
• To Buffer Start Addr(Hex) to 00000

• Memory Buffer should look like

• Got Device ID error
• Turn off ID check

• Device programmed/verified

Install CPU, ROM, RAM, ACIA

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

Test FTDI Serial

• Silkscreen swapped for TX, RX

• 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

• ExBasROM.hex - ROM file

ROM BASIC assembly listing

• AS9 was used to assemble the BASIC listing
• Grant wrote a serial handler to control the text I/O, along with suitable Control-C break handling
• Includes commands from the "Extended" BASIC ROM (from the "Extended BASIC Unraveled II" book)
• The ROM in the SBC is fully working with all the commands in the Standard and Extended ROMS that are applicable to the SBC
• Assembled using as9 (see link later on this page) with the following command...

as9 exbasrom.asm -now l s19

• *-now" suppresses warnings
• "l" produces a lst file
• "s19" produces an s19 hex file
• If you use as9, you will probably get a "Null pointer assignment" message when it completes
  • This can be ignored, and is a known bug with as9 that doesn't affect operation (according to the readme file that came with it)

Performance

• TeraTerm settings

• Test software

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

• Time ~52 secs

PCB Issues

Rev 2

• Fix Silkscreen on J3 (see above J3 FTDI cable section)
• Ordered 10 PCBs from JLCPCB

Rev 1

• Works
• Silkscreen J3 is wrong directions (TX/RX)

Mechanicals

Assembly Sheet

Rev 2

• SIMPLE-6809 Rev 2 Interactive BOM

Rev 1

• SIMPLE-6809 Rev 1 Assembly Sheet
• SIMPLE-6809 Rev 1 Interactive BOM