| C64 address decoding [message #209967] |
Wed, 19 June 2013 09:55  |
Michele
Messages: 59
Registered: February 2013
Karma: 0
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Member |
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Hi, I'm experiencing an RTC for C64, I need an address to make it visible so
need an address decoder maybe around $D200-$D300, but don't know how to
calculate/make it.
In my C64 there is a dual sid with address decoder built in, it use a 74139
with the following connections:
G1 of 74139 to CS of SID
A1 of 74139 to A8 of kernal
B1 of 74139 to GND
G2 of 74139 to CS of SID
A2 of 74139 to A5 of kernal
B2 of 74139 to GND
how to calculate the addresses that i will find at pins
1Y0-1Y1-1Y2-1Y3-2Y0-2Y1-2Y2-2Y3 ?
thanks in advance
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| Re: C64 address decoding [message #209968 is a reply to message #209967] |
Wed, 19 June 2013 19:02  |
Anton Treuenfels
Messages: 105
Registered: December 2011
Karma: 0
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Senior Member |
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"M1Ch3L3" <mailboxNOSPAM@piemmeweb.com> wrote in message
news:51c1b838$0$12828$5fc30a8@news.tiscali.it...
> Hi, I'm experiencing an RTC for C64, I need an address to make it visible
> so need an address decoder maybe around $D200-$D300, but don't know how to
> calculate/make it.
> In my C64 there is a dual sid with address decoder built in, it use a
> 74139 with the following connections:
>
> G1 of 74139 to CS of SID
> A1 of 74139 to A8 of kernal
> B1 of 74139 to GND
> G2 of 74139 to CS of SID
> A2 of 74139 to A5 of kernal
> B2 of 74139 to GND
>
> how to calculate the addresses that i will find at pins
> 1Y0-1Y1-1Y2-1Y3-2Y0-2Y1-2Y2-2Y3 ?
>
> thanks in advance
>
You might have better luck asking this question at www.6502.org, in the
"hardware" section.
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| Re: C64 address decoding [message #209969 is a reply to message #209967] |
Wed, 19 June 2013 19:25 |
Clocky
Messages: 1212
Registered: December 2011
Karma: 0
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Senior Member |
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M1Ch3L3 wrote:
> Hi, I'm experiencing an RTC for C64, I need an address to make it visible so
> need an address decoder maybe around $D200-$D300, but don't know how to
> calculate/make it.
> In my C64 there is a dual sid with address decoder built in, it use a 74139
> with the following connections:
>
> G1 of 74139 to CS of SID
> A1 of 74139 to A8 of kernal
> B1 of 74139 to GND
> G2 of 74139 to CS of SID
> A2 of 74139 to A5 of kernal
> B2 of 74139 to GND
>
> how to calculate the addresses that i will find at pins
> 1Y0-1Y1-1Y2-1Y3-2Y0-2Y1-2Y2-2Y3 ?
>
> thanks in advance
>
>
Do you know the addresses of the SID(s) (G1/G2) that the 74139 is
addressing?
From that you should be able to figure out the logical addresses on the
outputs as they are usually equally spaced, if that makes sense.
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| Re: C64 address decoding [message #209977 is a reply to message #209967] |
Fri, 21 June 2013 04:54 |
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Originally posted by: <silverdr
"M1Ch3L3" <mailboxNOSPAM@piemmeweb.com> wrote:
> Hi, I'm experiencing an RTC for C64, I need an address to make it visible so
> need an address decoder maybe around $D200-$D300, but don't know how to
> calculate/make it.
> In my C64 there is a dual sid with address decoder built in, it use a 74139
> with the following connections:
>
> G1 of 74139 to CS of SID
> A1 of 74139 to A8 of kernal
> B1 of 74139 to GND
> G2 of 74139 to CS of SID
> A2 of 74139 to A5 of kernal
> B2 of 74139 to GND
>
> how to calculate the addresses that i will find at pins
> 1Y0-1Y1-1Y2-1Y3-2Y0-2Y1-2Y2-2Y3 ?
>
> thanks in advance
To make a chip "visible", you need to generate _cs/_oe signals for the chip
whenever address bus is driven to a predefined value. While you can of
course process/watch all address lines and react whenever the range is of
what you want your chip to be visible at, much easier approach in machines
like the 64 is to find a chip which has its registers "mirrored" and use
those mirrored addresses (In case of an RTC, I would go for one of the
CIAs). In such case only a few lines have to be processed as the address
for the main chip is already decoded by pla.
--
SD!
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