PET REU 512Kb (1024Kb)
Conception
For the additional banking a second 6522 VIA must be added. We need three I/Os for switching A16-A18.
The unused ports are for future upgrades.
The second port is useful for a clock or building a fast serial with a max232.
Also a battery will be added for data retention. Newer SRAMs only need 1.5V supply voltage for this function.
Banking Basics
The 512Kx8 Brilliance Semiconductor BS62LV4006 will be switched into 8 banks. Each bank will storage up to 64Kb data.
Full address space will use in this case 16 lines (Cartridge port PIN B-U).
The pinout : BS62LV4006 /SC/SI/EC/EI/PC/PI -: PDIP32
+----------------+
A18 |1 * 32| VCC
A16 |2 31| A15
A14 |3 30| A17
A12 |4 29| WE
A7 |5 28| A13
A6 |6 27| A8
A5 |7 26| A9
A4 |8 25| A11
A3 |9 24| OE
A2 |10 23| A10
A1 |11 22| CE
A0 |12 21| D7
D0 |13 20| D6
D1 |14 19| D5
D2 |15 18| D4
GND |16 17| D3
+----------------+
A16 A17 A18 Bank
----+----+-----+------
0 0 0 0
1 0 0 1
0 1 0 2
1 1 0 3
0 0 1 4
1 0 1 5
0 1 1 6
1 1 1 7
Cartridge
The modified cartridge port. $8F00 must be changed to RESet. This I/O-address is in use for the SID-Chip.
So there is no need to keep this up. I/O1 ($8800) is the cartridge-box VIA. This line must be changed to
IRQ.
Also A0-A3 and PHI2 must be added to the expander. Datalines are not buffered by the 74245 anymore ! You have
to bridge the existing bus-tranceiver or switch this by an additional logic.
This is the major change. To use the old 128kb Cartridge the datalines must be buffered.
Coming Mem-Carts will include the 74245-driver.
Please visit the development page for the old circuit.
(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 IRQ 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 RESet J PA6
9 A3 K PA7
10 A2 L PB0
11 A1 M PB1
12 A0 N PB2
13 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
Development
We use the existing 6522 for switching the address lines. CA2 and CB2 will switch up to 4 ICs with a 74139.
So there are piggyback 2MB possible. The coming software will use 1024KB.
Address overview : $8800 Cartridge-Box VIA (address lines)
$8900 bus transceiver and SRAM (CS)
$8A00 additional 6522 VIA for banking (port A)
$8B00 ACIA (not in use yet)
Schematic
The first wild wired development-cartridge works.
The schematic shows the CPU-slot seen at the PET-SID PCB. Don't get confused about the pinout. You may replace
this connector with a 6502-socket. But remember you need the I/O-lines ($8800,$8900,$8A00).
PET-REU Schematic for PET-SID (CPU-SLOT)
PET-REU Schematic for 6502-Socket (decoded)
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At the backside you'll find the replaced
bus-transceiver. Shame on me for that. ;)
But this was the only way to fix the design mistake. Please remove the 74245 from the Cartridge-Box and bridge the 8 datalines.
The ACIA is not in use yet. It's only an addon for serial communication.
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SOURCE CODE
Setup Tool for PET-REU ACME-Source
PET-REU Setup PRG-Download
Your setup for the PET-REU. Formats all banks with $20.
The last distributed source was to bugged. I've kicked the verify.
Format 512KB Chip
!to "reuformat.prg"
*=$033c
;-------------------------------------------------------------------------------
;
; SYS 828 to start
;
; Formatroutine for PET-REU (only for CBM 3001 (ROMs) !)
;
; Compiler : ACME
;
; bin : 126 bytes
;
; This basic-routine is easy to modify. Use it stand-alone or as
; reconfigurable dropout for an option-rom.
;
; 19th,October,2K5 ; Bugfix: 22.October,2K5
;
;-------------------------------------------------------------------------------
; (c) M. Sachse , http://www.cbmhardware.de
; http://www.cbmpet.de
;-------------------------------------------------------------------------------
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 2 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program; if not, write to the Free Software
; Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
;
;-------------------------------------------------------------------------------
;Base addresses
via = $8800
datalatch = $8900
via_b = $8A00
BSOUT = $FFD2
banks = $0a
;---------------------------------------------------
; show text and setup via(s)
;---------------------------------------------------
lda #$93
jsr BSOUT ; clear screen
ldx #13
lda #<mes
sta $1F ; Text low
lda #>mes
sta $20 ; and high byte
JSR $CA23 ; show mes on screen
lda #255
sta via+2
sta via+3 ; ports to output
sta via_b+2
sta via_b+3
lda #00 ; set addr. $0000 in SRAM
sta via ; register B
sta via+1 ; register A
lda #204 ; CA2/CB2 : %00
sta via+12 ; choose RAM-IC 0
lda #00
sta banks
;---------------------------------------------------
; Looproutine for 8 banks
;---------------------------------------------------
bank lda banks
JSR $FDCD ; put one space between bank counter
lda banks
JSR $E775 ; show written bank
sta via_b+1 ; and set bank 0 (port a)
jsr ramcopy
lda banks ; read banks
cmp #07 ; 8 ?
bne bank
JSR $FDCD ; put one space between bank counter
lda banks
JSR $E775 ; show written bank
jmp end
;---------------------------------------------------
; 64K Format : Fillbyte : $00
;---------------------------------------------------
ramcopy sei
ldx #00
repump ldy #00 ; low addr. counter
pump lda #00 ; fillbyte
sta datalatch ; write byte to port
iny
sty via+1 ; register A : set low addr.
bne pump
inx
stx via ; register B : set high addr.
pcounter cpx #255 ; blocks
bne repump ; damned, we do 256x256 Byte = 65536 Byte (64KB)
cli
inc banks ; in 8 banks = 524288 words by 8bit
end rts
;---------------------------------------------------
mes !TEXT "REU FORMAT : "
!Byte $0d
..... and again under construction ....
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