Petscii Forums "PETSCII.COM" - RTC Option ROM for PETs

Leif Bloomquist
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RTC Option ROM for PETs
« Thread Started on Jun 12, 2006, 9:39pm »

Several people have asked me about this project, and I'm finally getting around to posting some details

Preamble: I have a nifty PET 8296 that someone gave me, and I was able to repair it (replace PLA with EPROM). I had to find a use for it, so I set it up as a simple database for my wife and I to keep track of what's in our chest freezer. (She thinks it's great, and it's better than the whiteboard which the cats kept erasing).

It's useful to have the items datestamped, so we can do simple searches like "do we have any pizza that's more than 6 months old?"

To start with we entered the date manually, but that became tedious. So I've come up with a rather simple way to keep track of the date when the power is off, and a way to retrieve it.

There are basically only two components required:

1. The BQ4830Y from Texas Instruments. This is a nifty Real Time Clock chip that "looks" like normal RAM to the computer. It even has the same pinout as a 27C128! Plus you get 32K of battery-backed static RAM for storing anything in. Reading the time is as easy as PEEKing the uppermost 8 bytes and doing some math. Crystal and battery are all built into the case.

2. Nicolas Welte's EPROM Adaptor .

When complete, they look like this:

[image]

Here it is installed in my PET Option ROM socket:

[image]

The one tricky part is setting the time. There's no R/W line going out to the option ROM sockets, and I believe the PLA wouldn't let you POKE to that address range anyway.

So I rigged up a circuit on my VIC20 and 8-Bit Baby board so that I could set the time. The VIC is a better choice than the C64, because the C64 PLA also prevents you from POKEing into external RAM.

[image]

In addition, I wrote a short ML routine (see below) to convert the BCD-encoded time into normal decimal values. This program gets stored in the BQ's RAM, and I can simply SYS to it and read the values.

[image]

So I can simply compile the program, load it with ,8,1 on my VIC, and presto it's in the battery-backed RAM and ready to use on the PET.

One limitation is that without installing switches on Nicolas' adaptor, you only get access to the upper 4K. But since the 32K version of the BQ was cheaper than the 4K version (!), that's not such a big deal.

Here's the source to the ML routine that converts the time.

Code:
; RTC Parser Code
; Leif Bloomquist - April 3, 2006

processor 6502 ; PET 8296

; Jump Table --------------------------------------------------------

; Parse
org $9c40,0 ;40000 decimal (Fill value=0)
jmp parse

; Print Message
org $9c4A ;40010 decimal
jmp print

; Code (Parse) --------------------------------------------------------

parse
;Set Read Mode
lda $9ff8
ora #$40
sta $9ff8

; Read Year (add 2000 to it in BASIC)
ldy $9fff
lda lookup,y
sta 0700 ;Inside the tape buffer - note decimal!

;Read Month
ldy $9ffe
and #$1f
lda lookup,y
sta 0701

;Read Date
ldy $9ffd
and #$3f
lda lookup,y
sta 0702

;Read Day of week
ldy $9ffc
and #$08
lda lookup,y
sta 0703

;Read Hours
ldy $9ffb
and #$3f
lda lookup,y
sta 0704

;Read Minutes
ldy $9ffa
and #$7f
lda lookup,y
sta 0705

;Read Seconds
ldy $9ff9
and #$7f
lda lookup,y
sta 0706

;Clear Read Mode
lda $9ff8
and #$BF
sta $9ff8

rts

; Code (Print) --------------------------------------------------------

print
ldy #$00
loop
lda message,y
beq done
jsr $ffd2
iny
jmp loop

done
rts

; BCD Lookup Table --------------------------------------------------------

org $9d00
lookup
dc.b    0
dc.b    1
dc.b    2
dc.b    3
dc.b    4
dc.b    5
dc.b    6
dc.b    7
dc.b    8
dc.b    9
dc.b    10
dc.b    11
dc.b    12
dc.b    13
dc.b    14
dc.b    15
dc.b    10
dc.b    11
dc.b    12
dc.b    13
dc.b    14
dc.b    15
dc.b    16
dc.b    17
dc.b    18
dc.b    19
dc.b    20
dc.b    21
dc.b    22
dc.b    23
dc.b    24
dc.b    25
dc.b    20
dc.b    21
dc.b    22
dc.b    23
dc.b    24
dc.b    25
dc.b    26
dc.b    27
dc.b    28
dc.b    29
dc.b    30
dc.b    31
dc.b    32
dc.b    33
dc.b    34
dc.b    35
dc.b    30
dc.b    31
dc.b    32
dc.b    33
dc.b    34
dc.b    35
dc.b    36
dc.b    37
dc.b    38
dc.b    39
dc.b    40
dc.b    41
dc.b    42
dc.b    43
dc.b    44
dc.b    45
dc.b    40
dc.b    41
dc.b    42
dc.b    43
dc.b    44
dc.b    45
dc.b    46
dc.b    47
dc.b    48
dc.b    49
dc.b    50
dc.b    51
dc.b    52
dc.b    53
dc.b    54
dc.b    55
dc.b    50
dc.b    51
dc.b    52
dc.b    53
dc.b    54
dc.b    55
dc.b    56
dc.b    57
dc.b    58
dc.b    59
dc.b    60
dc.b    61
dc.b    62
dc.b    63
dc.b    64
dc.b    65
dc.b    60
dc.b    61
dc.b    62
dc.b    63
dc.b    64
dc.b    65
dc.b    66
dc.b    67
dc.b    68
dc.b    69
dc.b    70
dc.b    71
dc.b    72
dc.b    73
dc.b    74
dc.b    75
dc.b    70
dc.b    71
dc.b    72
dc.b    73
dc.b    74
dc.b    75
dc.b    76
dc.b    77
dc.b    78
dc.b    79
dc.b    80
dc.b    81
dc.b    82
dc.b    83
dc.b    84
dc.b    85
dc.b    80
dc.b    81
dc.b    82
dc.b    83
dc.b    84
dc.b    85
dc.b    86
dc.b    87
dc.b    88
dc.b    89
dc.b    90
dc.b    91
dc.b    92
dc.b    93
dc.b    94
dc.b    95
dc.b    90
dc.b    91
dc.b    92
dc.b    93
dc.b    94
dc.b    95
dc.b    96
dc.b    97
dc.b    98
dc.b    99
dc.b    100
dc.b    101
dc.b    102
dc.b    103
dc.b    104
dc.b    105
dc.b    100
dc.b    101
dc.b    102
dc.b    103
dc.b    104
dc.b    105
dc.b    106
dc.b    107
dc.b    108
dc.b    109
dc.b    110
dc.b    111
dc.b    112
dc.b    113
dc.b    114
dc.b    115
dc.b    110
dc.b    111
dc.b    112
dc.b    113
dc.b    114
dc.b    115
dc.b    116
dc.b    117
dc.b    118
dc.b    119
dc.b    120
dc.b    121
dc.b    122
dc.b    123
dc.b    124
dc.b    125
dc.b    120
dc.b    121
dc.b    122
dc.b    123
dc.b    124
dc.b    125
dc.b    126
dc.b    127
dc.b    128
dc.b    129
dc.b    130
dc.b    131
dc.b    132
dc.b    133
dc.b    134
dc.b    135
dc.b    130
dc.b    131
dc.b    132
dc.b    133
dc.b    134
dc.b    135
dc.b    136
dc.b    137
dc.b    138
dc.b    139
dc.b    140
dc.b    141
dc.b    142
dc.b    143
dc.b    144
dc.b    145
dc.b    140
dc.b    141
dc.b    142
dc.b    143
dc.b    144
dc.b    145
dc.b    146
dc.b    147
dc.b    148
dc.b    149
dc.b    150
dc.b    151
dc.b    152
dc.b    153
dc.b    154
dc.b    155
dc.b    150
dc.b    151
dc.b    152
dc.b    153
dc.b    154
dc.b    155
dc.b    156
dc.b    157
dc.b    158
dc.b    159
dc.b    160
dc.b    161
dc.b    162
dc.b    163
dc.b    164
dc.b    165

message
dc.b 210,212,195," CHIP IS PRESENT.", $0d, $00

« Last Edit: Jun 12, 2006, 9:56pm by Leif Bloomquist »

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pyrofer
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Re: RTC Option ROM for PETs
« Reply #1 on Jun 13, 2006, 4:23am »

That is great.
You put a lot of work into this with great results! Why dont you add a serial barcode scanner to enter the product details for you

Also, if you put the expiry date when you log in food you can use it for the fridge to tell you when to dump stuff you forgot was in there. At the back. Festering.

More photos of the pet please! I want to see it running, and some better inside shots.

Thanks for sharing this with us all!

« Last Edit: Jun 13, 2006, 4:23am by pyrofer »

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Please visit my Project site at,
www.pyrofersprojects.com

David Murray
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Re: RTC Option ROM for PETs
« Reply #2 on Jun 13, 2006, 8:25am »

Oh lord.. that is just too darned simple. I spent two weeks trying to construct a PCB for one of those regular DALLAS RTC like go in a regular PC motherboard. I was trying to make it work on my C64 or my Plus/4. I only got it working partially. It would read correctly about 80% of the time, the rest of the time would give me eroneous numbers. So I gave up.

This is great. You could stick this in a Plus/4's internal socket (after you remove the crappy 3-plus-1 software) with the only needed modification being that you would need to run a wire for the read/write pin from the CPU (so you could update the time)

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Leif Bloomquist
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Re: RTC Option ROM for PETs
« Reply #3 on Jun 13, 2006, 8:32am »

Haha, a few people have suggested the barcode scanner. Maybe someday.

Here's a picture of the PET.
[image]

There are a few pictures of the innards here, plus pictures of the Greek character set that's installed.
http://www.jammingsignal.com/8296/pics/

Last but not least, here's the circuit for setting the time on the VIC. This was mostly designed by Brian Lyons.
[image]

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