65C02 CPU + Real Time CLock

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 Guus Assmann (who should be well known via SAG* or ABBUC) talked at the JHV** 2002 about one of his Atari 8Bit projects. Because it is a very interesting one, I have done this page for him. All required files (e.g. schematics and routing) can be found on this page below.
For questions, feedback, etc. please contact the developer Guus Assmannn via Email  (dutch, german, english language). The Project:

65C02 - A new CPU inside the Atari XL/XE + a Real-Time-Clock

 We will replace the CPU 6502C in the Atari with a 65C02. Furthermore we add a Real Time Clock and  a  Parallel-Printer-Port and leave options for an Upgrade up to 65C816 CPU.


   Pictures from 65C02-Board

   A new CPU, how and why?

   Schematic and Partlist

   The 65C816 Upgrade

   Download and Email

   Other Projects of Guus Assmann

Another Site for the 65C02 on http://www.retrobits.net  => Atari 8-bit => Projects => XL/XE Alternate CPU

*  SAG => Foundation of Atari Users in the Netherlands  /  ABBUC => Atari Bit Byter User Club in Germany

** JHV = "Jahres-Haupt-Versammlung", the name for the annual meeting (and atari-fair) of the german club ABBUC

And here some Pictures from the dutch "Atari-Magazin" in 1987:


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
    (I'll check).
 - 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.

This Text

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)

65C02 Upgrade:

  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

This Text

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
    as PostScript  ( 133.5 KB ) or
    as PortableDataFormat  ( 186,5 KB ) or
    as JPEG-Bild   ( 882 KB only Schematics and Parts )

Download of Partlist
    as Text-File   ( 1 KB )

Download of the driver software for the RTC (Pay attention to the comments in the source-text!)
    as Image-(ATR)-File   Atari-Disk-Image with sources and compiled data-files,  ( 20 KB )
    as Text-File   sources for MAC/65 assembler and basic-listing  ( 6,6 KB )
    as Atari-File      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 myatari.net
Neue Floppy für den Atari 8-Bit twiki by strotmann.de

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65C02 CPU + Real Time CLock

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