External Memory Problem

[@UAE]

Hi all
i install the 512 External memory for my a500+ .
but the battery life over ..
how can i disable the battery or bypass it and use which is on a500+ board and which also running fine without external Memory ...

The problem i have is the date .. its stuck on 92 ..

but without this Memory dates shows right ....

thank you

[RetroMan]

Hmmm, normally an A500+ isn´t capable of using the normal A500 mem expansions, you need a 1MB mem expansion ! Normal A500 expansions won´t work AFAIK ! Is the memory correct after inserting it ? Should be 1,5 MB then ....

[@UAE]

Yes its ok .. and working fine
except the date .

i remove the battery also same ..

[rlake]

So, am I right in that you're saying that you want to disable the date function of the external device (no battery) because it's overriding the internal device's date (with a battery)? If so, I'd probably try a battery in the external device first to see if there's some sort of hardware fault. Other than that, are there any jumpers on the board you could try?

Presumably if it's mapping into the same address space as the other real time clock there's the possibility that cutting a track on the PCB for the external clock's enable line... but hey, I wouldn't try that unless I really knew what I was doing!

[@UAE]

Yes there is a Jumper .. but i tried and disable it but same problem .. is priority to read the date on motherboard or other external board ..

sorry i dont have much experience in Amiga Hardware ..

[rlake]

Originally posted by @UAE
is priority to read the date on motherboard or other external board ..

Well, in theory when there's a conflict it could be either - it just happens to be that the external device wins. Unfortunately, I can't say why that is.

The only solution I can think of is to stop it reacting to calls to read the clock. Without knowing more about the device I can think of no way to explain how to do this without potentially breaking the RAM as well as the clock. Sorry. :(


sorry i dont have much experience in Amiga Hardware ..

Same here but I was taking a reasonable guess by considering what I've been taught in computer hardware class. I'll have more first hand experience when I get delivery of my own A500/A590 that needs a bit of work to get a joystick port functioning.

[rlake]

* This only guidance, this does not necessarily apply to an external expansion. Sorry if this is not understandable!

OK, a quick look at the A500 schematics / hardware reference later...

There is a schematic for what appears to be a "standard" real time clock. This contains enough information to describe what's going on.

In an A500, the real time clock maps into address range DC 0000 - DC FFFF. So, in your case there are 2 devices looking to see if they are the clock. You want to stop the external one performing this check, or reacting to it.

The address check can be made in hardware quite cheaply by looking for a pattern of "11011100" on 8 wires. If that's the case, the device should send clock data. However, in the case of the Amiga it is even cheaper and uses just 4 wires, to cover the range D0 0000 - DF FFFF! Therefore, it needs some other way to tell it if it should reply with data or not, or else it would interfere with the custome chips!

From the diagram I have, the chip is a "MSM62428" device. In addition to the address and data that you shouldn't mess with, it has 3 important wires:

_XCLKRD: Says when the chip should reply with data.
_XCLKWR: Says when the chip should store data.
_XCLKCS: Says when the chip is enabled. * This wire overcomes the 4 wire address "hack".

So, the best bet is disabling the clock by finding the _XCLKCS signal (I think it's pin 2 of the chip). Then, since it's "active low" (denoted by "_" in "_XCLKCS") you should break the track and hook a wire between the pin and +5V.

I hope you understand what I'm saying here... if you can locate the correct pin you're in with a chance. Hopefully the board you have uses a similar clock system to the one I've described... look for something with similar characteristics: a chip with 4 address wires, 4 data wires and 3 control wires - it'll stand out from the RAM chips swear. If you're very lucky you'll follow that chip select wire and find a jumper... otherwise the solder hack would be necessary. :(

If in any doubt don't do anything at all. Oh, and if you can take a detailed picture of the board may be able to help further.

[ElectroBlaster]

I always thought A500+'s had an internal battery keeping the date active?

and as i have never fitted an a500 mem expansion to an 500+ ive never run into this problem!