2 ql's and roms ?

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jdavis6809
ROM Dongle
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2 ql's and roms ?

Postby jdavis6809 » Fri Sep 13, 2019 3:47 pm

hello,

have 2 ql's

question 1 first ql issue 5 m/b

has jm rom can it be replace with js rom with no mods ?

question 2 2nd ql issue 5 m/b

has jm roms but one rom is piggy backed with two roms in one socket with one pin sticking out connected to the m/b
can be removed and replaced with normal jm rom ?

regards

john davis uk


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tofro
QL Wafer Drive
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Re: 2 ql's and roms ?

Postby tofro » Fri Sep 13, 2019 4:48 pm

jdavis6809 wrote:hello,

have 2 ql's

question 1 first ql issue 5 m/b

has jm rom can it be replace with js rom with no mods ?


Yep, with no problems at all. Just plug in the new ROM set.
Note in case you use EPROMs instead of original ROMs, you need to change some jumper settings on the board. But original Sinclair JS ROMs can just plug in.

jdavis6809 wrote:
question 2 2nd ql issue 5 m/b

has jm roms but one rom is piggy backed with two roms in one socket with one pin sticking out connected to the m/b
can be removed and replaced with normal jm rom ?

That is an earlier board version, I think. Very probably the stacked chips are not ROMs, but rather EPROMs.
Does the board have an IC17 equipped?

Basically, there are two ways to upgrade this board to a new OS:

  1. Leave the piggy-pack thing as is, burn a set of EPROMs with the lower 16k in the left one, the upper 16k half and half into the 2 stacked chips (lower addresses in the bottom chip, obviously needs some soldering, keep JU1-4 as-is)
  2. Upgrade board revision to newer version:
    1. remove IC17
    2. remove the flying lead (the one conected from the pin of IC33)
    3. set JU2, JU3 and JU4
      install new ROM set (2x16k)

An explanation what the issue 5 board supports in terms of ROM/EPROM combinations and required jumper settings can be found in the bottom-right text box of the issue 5 schematics

Easiest thing is: Find yourself a Tetroid ROM switcher. This also allows you to change ROM versions on the fly.

Tobias


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Pr0f
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Re: 2 ql's and roms ?

Postby Pr0f » Fri Sep 13, 2019 6:23 pm

You can also solder 2 ROM's on top of each other if they are a set, as both sockets are in fact wired the same way, but the jumpers need to be wired for the 2 ROM setup - the advantage of doing this is it keeps one ROM socket free, for QL-SD or similar interfaces.


jdavis6809
ROM Dongle
Posts: 16
Joined: Mon Jan 09, 2017 3:16 pm

Re: 2 ql's and roms ?

Postby jdavis6809 » Fri Sep 13, 2019 9:51 pm

hello,

thanks for replies

the ql with stacked roms are eproms in one socket and a single eprom in the next socket so both are occupied
I understand what has been done, i thought that masked roms were always used ?

john uk


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Pr0f
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Re: 2 ql's and roms ?

Postby Pr0f » Fri Sep 13, 2019 10:56 pm

Early versions of the QL had a 3rd ROM in the ROM port and the 2 internal ROM sockets filled - these were 16K ROM's or EPROMS as the original intention was to get the OS and BASIC into 32K, but the ROM grew to 48K.

The ROM dongle was moved internally, hence the piggy backed ROM's and flying lead - each EPROM is 16K in size. This then migrated into a 32K ROM and a 16K ROM, each having identical pin out - so the ROM''s can be stacked or placed in either socket. The Chip select of one ROM is high, the other is low, so both can use the same line



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