More PET stuff

PET REU (RAM AND EXPANSION UNIT)

You may also call it cartridge slot. All hardware-design, soldering, coding and translation in english ;-) is done by myself. Some credits must go to Jogi (vic20.de) for hints and help with the glue logic.

The main theory

In the CBM PET 2001-N/3001 you'll find some unused I/O-space from $8800 up to $8FFF. The main logic decodes out of this range 8 I/O-lines. $8800 is in use for the additional VIA 6522. The two ports and four handshake-lines are connected to the cartridge-port. You may use it for addressing RAMs oder build anything else.
The second address $8900 is your port for the datalines. For building the adaptor you will only need 2 74138 demuxers, a 74245 bus transceiver and the 6522 VIA.

The Schematic without cartridge-port : Schematic. JP1 is the CPU connector. You have to get the signals from the CPU. Solder some wires or build an adaptor but don't use wires longer than 20cm. This equals to 7-8 inch. Otherwise the signals will flicker and you'll lose bytes while transfering .

The Cartridge-Slot (Prototype)

Cartridge-Port

(View : solder side)
                  1                   2 
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2

A B C D E F H J K L M N P R S T U V W X Y Z


 Pin  Signal                Pin  Signal

  1   I/O7 $8E00             A   GND
  2   I/O1 $8800             B   PA0
  3   I/O2 $8900             C   PA1
  4   I/O3 $8A00             D   PA2
  5   I/O4 $8B00             E   PA3
  6   I/O5 $8C00             F   PA4 
  7   I/O6 $8D00             H   PA5  
  8   I/O8 $8F00             J   PA6
  9   NC (A3)                K   PA7
 10   NC (A2)                L   PB0 
 11   NC (A1)                M   PB1  
 12   NC (A0)                N   PB2  
 13   NC (PHI 2)             P   PB3   
 14   R/W                    R   PB4 
 15   D7                     S   PB5 
 16   D6                     T   PB6 
 17   D5                     U   PB7  
 18   D4                     V   CB1
 19   D3                     W   CB2
 20   D2                     X   VCC +5V=
 21   D1                     Y   CA1
 22   D0                     Z   CA2
      
 Datalines are buffered ($8900) and the VIA base is $8800. Some pins
 are not connected this time (pin 9-13).

The first 128KB SRAM-Cartridge

This uses some old Winbond W24257 RAMs in 4 banks. The banking is switched by a half 74139. Keep in mind : CS must be switched to access the rams. You have only to connect the 2 VIA-ports as addresslines and the dataport to the in line wired SRAMS.
OE must connected to ground, WE to R/W and the CS-lines will be switched by the 74139 ports. Pin 1 of the 139er demuxer is connected to $8900 (I/O2), Pin 2 to CA2 and Pin 3 to CB2. The four CS-lines are Pin 4-7.

128KB SRAM Expansion

The Banking

 
   CA2 |  CB2  |  Bank  
 -----------------------
    0  |   0   |    0 
    0  |   1   |    1 
    1  |   0   |    2          
    1  |   1   |    3

The final "Side car" :*)

The case of an old printer buffer houses now the pcb. There is enough space for future ideas.

Software

A first test :

poke 34816+2,255 : poke 34816+3,255
poke 34816,0 : poke 34816+1,0

This switches the ports to output and set the latches low (address $0000).

Now poke a value : poke 34816+256,32

D=peek(34816+256): ?D will bring (hopeful) the value back. Play around with
the addresses and banks to check your circuit.

!to "petreu.prg"
*=$033c
;---------------------------------------------------
;
; Compiler : ACME
;
; Poke 877,blocks : Poke 934,blocks to configure mem pumps
;
; SYS 828 to copy into ram-bank and sys 884 to fetch
;
; raw copy for whole free basic mem (32K machine) 
;
;---------------------------------------------------
;Base addresses

 via       = $8800
 datalatch = $8900
 
;---------------------------------------------------
; copy into sram
;---------------------------------------------------
                 lda #255
                 sta via+2
                 sta via+3           ; ports to output
                 lda #00             ; set addr. $0000 in SRAM
                 sta via             ; register B
                 sta via+1           ; register A
                 lda #04             ; restore value
                 sta pump+2   
ramcopy          sei
                 ldx #00
        repump   ldy #00             ; low addr. counter
          pump   lda $0400,Y 
                 sta datalatch       ; write byte to port    
                 nop:nop:nop:        ; sta $8000,y : some peep-show for the coder
                 iny
                 sty via+1           ; register A : set low addr.
                 bne pump
                 inc pump+2          ; inc source high byte 
                 inx
                 stx via             ; register B : set high addr.
     pcounter    cpx #124            ; blocks
                 bne repump    
                 cli
                 rts   
                 nop:nop:nop         ; for the coder ;)
;--------------------------------------------------
; ... and bring it back 
;--------------------------------------------------
                 lda #255
                 sta via+2
                 sta via+3
                 lda #00
                 sta via               ; register B
                 sta via+1             ; register A
                 lda #04 
                 sta target+2   
backcopy         sei
                 ldx #00
         rpump   ldy #00               ; low addr. counter
         pump1   lda datalatch
   target        sta $0400,Y
                 nop:nop:nop:          ; sta $8000,y  : some peep-show for the coder
                 iny
                 sty via+1
                 bne pump1
                 inc target+2          ; inc high byte 
                 inx
                 stx via               ; register B : set high addr.
     pcounter1   cpx #124              ; blocks                  
                 bne rpump    
                 cli
                 rts

REU Software
Software for the option rom at $9000. You'll able to copy the whole memory from $0400 -$7FFF in the chosen bank. Sure, you can also bring it back. ;)
The software will relocate the copy-routine to $033c. So the whole basic mem is free for your tools.
You can't use basic programs with this beta software ! This lack will be fixed with the next version. You may delete or use the XLOAD in the menu. It is a older project to transfer bins from a DOS PC to the PET. Source is included and under GPL license.

Downloads

PET REU 128KB Software for ROM $9000 - public beta 1

Letzte Änderung: 2019-01-04 13:05:21