Re: Tempest memory

One small correction.

> On the 6502 a word is 16 bits or two 8 bit bytes

On the 6502, a word is 8 bits.

On Mon, Oct 10, 2011 at 8:34 PM, vectorlist-steve <
vectorlist@arcadehacking.com> wrote:

> **
> Comments inline Kevin...
>
>
>
> On 10/10/2011 5:44 AM, Kevin Moore wrote:
>
> Ugh... Thanks. After seeing the memory map laid out, ie
> 0x2000 - 0x23FF --> M3 (D0-3) and M4 (D4-7)
> It make sense now.. Vram 0 M3 and M4.
>
>
> M4 is the suspect since you were having issues with D7. If you have a
> spare 2114 ram on hand, hold it on top of M4 with all of the pins making
> contact and see if the new ram resolves your issue. This test is not 100%
> guaranteed but if the error is resolved then you KNOW which chip needs to be
> replaced.
>
>
> So by doubling the ram like they do, you can now write an 8 bit word
> correct?
>
> So for example, an 8 bit word will get split between M3, and M4
>
>
> Yes, two 4 bit nibbles is one 8 bit byte
>
> On the 6502 a word is 16 bits or two 8 bit bytes
>
>
>
>
> I'm thinking I should have paid more attention in microprocessor class in
> college some 20 years ago.
>
> Thanks for the help.
>
> Kevin
>
>
>
>
> On Mon, Oct 10, 2011 at 12:00 AM, vectorlist-steve <
> vectorlist@arcadehacking.com> wrote:
>
>> Check out page 5 of the Tempest Drawing Package (DP-190 2nd Printing)
>>
>> Decoding is grouped in the Vector-Generator Address Selector box.
>>
>>
>> VRAM
>> ---------------
>> 0x2000 - 0x23FF --> M3 (D0-3) and M4 (D4-7)
>> 0x2400 - 0x27FF --> L3 (D0-3) and L4 (D4-7)
>> 0x2800 - 0x2BFF --> K3 (D0-3) and K4 (D4-7)
>> 0x2C00 - 0x2FFF --> J3 (D0-3) and J4 (D4-7)
>>
>> VROM
>> ---------------
>> 0x3000 - 0x37FF --> N/P3 (D0-7)
>> 0x3800 - 0x3FFF --> R3 (D0-7)
>>
>>
>>
>>
>> On 10/9/2011 9:34 PM, Kevin Moore wrote:
>>
>>>
>>> Ok, so I don't often come across a memory problem that the tempest self
>>> test doesn't point me to.
>>>
>>> But today my fluke is showing me a decode error at 2c00 bit 7 . Which is
>>> affecting vectors in game.
>>>
>>> I'm trying to figure out which RAM chip is giving me problems short of
>>> pulling all the chips.
>>>
>>> Are there any documents out the explaining how memory is allocated and
>>> used on Atari boards?
>>>
>>> I would really like to learn how to find the correct chip or I assume
>>> narrow down to two chips
>>>
>>> Kevin
>>>
>>
>

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Received on Tue Oct 11 00:59:08 2011