And here some Pictures from the dutch "Atari-Magazin" in 1987:
Note: the ribbon cable in the pictures is to support a memory upgrade, and not necessary for this mod.
Pieces of the Board
Design history: (the original Text)
The schematics of the old 400 / 800 contain the CPU part already. So this was just simple to do. And back in 1986 it was expensive to buy an Atari CPU. The 65C02 was less expensive and could also be buffered. This is useful if you want to add more hardware to the system. And more hardware was something that was wanted. And when a PCB has to be designed, why not do something more. So also a Real Time Clock was added. But this called for an extra PIA. This could be done in the cartridge port also, but this would be used up then. And if someone decides to open up his computer, why not do more at once. This extra PIA would then have one port left. In turn it would be good to use this port for a centronics printer driver. This driver would be a chance to call for a contest.
Why hardware was needed? It's good material to get a magazine filled. And the ATARI Magazine, by the SAG (Foundation of Atari Users in the Netherlands) could use some good information. In the interest of 7000 users it's nice to help keep prices low. This has been the philosophy of the SAG all the time. If you publish something and offer parts, it keeps prices low.
A new CPU ? How and Why ?
Characteristics from the Board
- A 65C02 CPU with buffered address and data bus
- A second PIA. One port with a RTC. The second port with buffering to create a printer port.
- Device driver software for the Real Time Clock. (Including source code- only on paper yet, is tested.)
- Board replaces the original CPU and PIA. Both have to be removed, the PCB occupies their previous location, PIA can be reused on the PCB.
- The CPU may also be replaced by a 65C816 with some minor modifications
- PCB may be cut to only use CPU or PIA.
Why replace the CPU ?
- The original 6502 and also the ATARI 6502C have some minor bugs.
- The 65C02 fixes these and also adds some very useful instructions.
- Also now the CPU address and data busses are buffered.
- The 65C02 is CMOS and draws less current.
- Some Atari CPU's, manufactured in Mexico are defective. They are temperature sensitive and make the computer hang
Why a second PIA?
- To be able to use the RTC and add a printer port, without compromising compatibility. If the extension is not wanted, don't load drivers and it's not there.
Disadvantage of the 65C02 CPU
Programs that use illegale Opcodes (means many Demo Programs and some newer Games) works not with the 65C02 CPU!
Click on the Picture for a larger view (300dpi, 3265 x 2227 Pixel, 889 KB)
Explanation of Schematics
Items required: (PCB may be cut to only use CPU or PIA)
1 x IC 65C02 CPU
1 x IC 74LS02
1 x IC 74LS74
2 x IC 74LS244
1 x IC 72LS245
3 x Drossel 10uH
3 x Widerstand 1 Ohm
2 x Kondensator 100nF
1 x Stecker 40 pins DIL oder qualitäts-Sockel mit Drähte
1 x IC MSM5832 RTC Chip (OKI)
1 x IC 6520 oder 6821 (der zweite ist der vom Atari)
1 x IC 74LS04
5 x Widerstand 100K
1 x Widerstand 1K
1 x Kondensator 22 pF
3 x Kondensator 100 nF
1 x Drehkondensator 5-20 pF
1 x Quartz 32,768 kHz Uhrenquartz.
1 x Diode D1= AA119 oder andere Germanium oder Schottky Diode.
1 x Diode D2= 1N4148
1 x Elko 10uF / 16V
1 x Stecker 40 pins DIL oder qualitäts-Sockel mit Drähte.
1 x 74LS244
Upgrade with the 65C816 CPU
Die 65C816 CPU might give you further advantages:
The 65C816 CPU can be used with up to 14Mhz which is an enormous increase in power!
The 65C816 CPU has a linear adress range of 16MB. In 24 bit adressing, the upper 8 bits are banks, meaning 256 banks of 64kbytes each. But here is the question on how to make this compatible to the 130XE standard of port B.
The 65C816 CPU has two operation modes:
One emulation mode, where (after Reset) all instructions and adresses (adress modes) are usable.
Next a native mode, which allows the full use of the CPU via 16bit registers and block-move instructions.
These are the main advantages. The disadvantages are for example, that if doubling the clock speed the clock cycles have to be synchronized (extremely difficult!). The actual developer phase by Guus is a 65C816 which runs at normal clock speed.
Pins 1, 5, 7, 35, 38, 39 of the CPU do not connect.
Pin 3 via Pull up Resistor 10KOhm to +5V.
Pin 36 to Pin 5 from 74LS74 (latching Halt Signal)
The next step ist to double the clock speed of the CPU, whereby the clock cycles have to be synchronized.
Download of the required Files and Data:
The pcb-layout is different from that of the older original. Pay attention on the new list of parts.
Download of the schematics, pcb-layout and parts
( 133.5 KB ) or
( 186,5 KB ) or
( 882 KB only Schematics and Parts )
Download of Partlist
( 1 KB )
Download of the driver software for the RTC (Pay attention to the comments in the source-text!)
Atari-Disk-Image with sources and compiled data-files, ( 20 KB )
sources for MAC/65 assembler and basic-listing ( 6,6 KB )
compiled data-file and basic-file ( 3,3 KB ) (SETCLOCK.BAS new at 11/06/2003)
Full documentation and all required manuals are present. If you have questions or feedback, then please contact the developer
Guus Assmann via Email
(dutch, german or english language)
Other Projekts of Guus Assmann:
USB-Port for the Cartridge Slot
twiki by strotmann.de,
USB-Port for the Cartridge Slot
Neue Floppy für den Atari 8-Bit
twiki by strotmann.de