SIMPLE-6502

Features

• Build of Grant Searles's Simple 6502 CPU
  • Runs Microsoft (OSI) BASIC
• 6502 CPU
• 0.9216 or 1.8432 MHz clock
• 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

Chip Set

• Ordered from Ebay

• Used these parts:

References

• Grant Searles's Simple 6502 CPU - This build
• 6502.org
  • Example builds
  • Source Code Repository
  • Datasheets
• 6502 PRIMER: Building your own 6502 computer - Great resource with a lot of design information
• Build Your Own 6502 Computer

Design

• CPU

• EPROM/EPROM

• SRAM

• Clock

• UART

• FTDI

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 - Speed Select Jumper

• 1-2 - 0.92 MHz
• 2-3 = 1.8432 MHz

J3 - FTDI / TTL Serial

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

J4 - 5V Power

• 2x4 header

J5 / J6 - EPROM/EEPROM Select Jumpers

27512	27256	28C256	27128	2764	28C64	PIN		PIN	2764	28C64	27128	28C256	27256	27512
A15	VPP	A14	VPP	VPP	N/C	1		28	VCC	VCC	VCC	VCC	VCC	VCC
A12	A12	A12	A12	A12	A12	2		27	PGM	WE*	PGM	WE*	A14	A14
A7	A7	A7	A7	A7	A7	3		26	A13	N/C	A13	A13	A13	A13
A6	A6	A6	A6	A6	A6	4		25	A8	A8	A8	A8	A8	A8
A5	A5	A5	A5	A5	A5	5		24	A9	A9	A9	A9	A9	A9
A4	A4	A4	A4	A4	A4	6		23	A11	A11	A11	A11	A11	A11
A3	A3	A3	A3	A3	A3	7		22	OE*	OE*	OE*	OE*	OE*	OE*
A2	A2	A2	A2	A2	A2	8		21	A10	A10	A10	A10	A10	A10
A1	A1	A1	A1	A1	A1	9		20	CE*	CE*	CE*	CE*	CE*	CE*
A0	A0	A0	A0	A0	A0	10		19	D7	D7	D7	D7	D7	D7
D0	D0	D0	D0	D0	D0	11		18	D6	D6	D6	D6	D6	D6
D1	D1	D1	D1	D1	D1	12		17	D5	D5	D5	D5	D5	D5
D2	D2	D2	D2	D2	D2	13		16	D4	D4	D4	D4	D4	D4
GND	GND	GND	GND	GND	GND	14		15	D3	D3	D3	D3	D3	D3

JP1 - CPU Pin 1

• Install if CPU is not a WDC 65C02 or WDC 65C816

Software

• Link to Grant's files
• Source code
  • osi_bas.s <== the Microsoft OSI BASIC and I/O routines SOURCE all in a single file. My I/O routines are at the end of it.
• Files to allow the source to be assembled on a Windows based machine
  • assemble.bat <== double click to assemble osi_bas.s and link to binary file "osi_bas.bin". This should be exactly 16K
  • osi_bas.cfg <== configuration file for the linker (ensure ORG and entries in this file match if you change any)
  • ca65.exe <== the assembler from the cc65 package. Use this. The new version on the cc65 site crashes!
  • ld65.exe <== linker from the cc65 package
• Output files
  • osi_bas.bin <== the ROM fine in pure binary
  • osi_bas.lst <== Assembly listing file
  • rom.hex <== the ROM fine in standard INTEL-HEX format
• To allow simple re-assembly, extract all files to the same folder
  • Freeware utilities are available to convert the "bin" file to HEX or s19 (etc) - use your internet search tool to find
• All source code, assembler binaries and the HEX dump of the ROM is here
  • It is in standard INTEL-HEX format for uploading to a suitable programmer.

Mechanicals

Checkout

• SST27C256 EEPROM
  • 32 KB part
  • Using first 16KB of EEPROM
  • Program using TL-866ii plus programmer
  • File = ROM.hex
  • J5 EEPROM pin 1 = VPP = VCC or GND
    • Jumper J5:2-3
  • J6 EEPROM pin 27 = A14 = GND
    • Jumper J6:2-3

Assembly Sheet

• SIMPLE-6502 Rev 1 Assembly Sheet
• Interactive BOM