Caple C871i Manual do Utilizador descarregar pdf (Página 175)

100

101

Apple II Computer Info

switching. Decoding the slot ROM (Cnxx) could force a certain bank (such as

bank zero which would presumably always be there). The PLD could also

convert the R/W line to /OE and /WE lines for memory.

You don't need to use all this space, but at least make it available...

Lets see...

To make all of this happen, you need /IOSEL, /IOSTRB & /DEVSEL for the 3

memory spaces

you need the 8 data bus lines to latch a bank number

(if you wanna make it simple make this read only)

A7:0 can go straight through to the memory chips...

A10:8 need to be latched (and driven) if you want to

force Cnxx accesses to a certain bank

you need to produce the high 8 address lines

(latched from the data bus/forced by /IOSEL)

you need to produce at least one /CS line

you need to convert R/W into /OE and /WE

adding that up you get 3 + 8 + 0 + (3 + 3) + 8 + 1 + (1 + 2) = 29 available

I/Os

This will fit comfortably in a 44-pin PLCC (socketable) package for under

$10 and will address all locations ('cept for the 256 CFFF locations (one in

each bank)) of a 512Kx8 FLASH (non-volatile memory) or SRAM. Smaller parts

will just 'wrap around in the available banks.

There are still outputs available in the same package for decoding other

locations in the C0[n+8]x range for other devices or purposes.

If you want to get fancy you could use the 7M clock to generate /CAS and

/RAS signals for DRAMs but this would require a larger package.

Going to a 68-pin PLCC package (or 84-pin PLCC) would give you enough I/Os

to decode almost anything.

If you were to produce some generic 'application-specific' logic parts you

might as well do it properly...

cheers

ntt@dove

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From: [email protected] (David Wilson)

Newsgroups: comp.sys.apple2

Subject: Re: Hardware Project

Date: 16 Nov 98 22:03:27 GMT

Organization: University of Wollongong, Australia

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Apple II Computer Technical Information : Apple II Family Hardware Info

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Caple C871i Manual do Utilizador Página 175

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