A500 trapdoor memory: free design

[Nbdy]

Bought an ACA500+, The thing is working with this ram expansion ...

Only the problem is that i recognizes only 1MB of slow ram ... (the 1MB chip is present)

Should this be like that, does the ACA reduces the ram, or should it still be 1.5MB of slow ...

Can someone confirm that who also have the same confg, if someone have it ???

[Negan]

I bought this memory expansion for the Amiga500+ to get 2MB chip RAM. It works wonderfully. I would like to mount an RTC on the small PCB. What do you need for this extension? the PCB is only partially assembled. I also have this RAM expansion on the normal Amiga 500, with 2.5MB incl. Gary adapter. Here the PCB is fully populated. I just want to have a working battery on it. Is there any way to do that? I ordered this battery holder from Amigastore.eu in the hope of being able to mount it.

[keithamiga1200]

Does anyone have the gerbers for RevB6 and RevC, without the Gary board? (The ones Pete has linked, have the Gary PCB attached).

[Nbdy]

Originally Posted by Negan

I bought this memory expansion for the Amiga500+ to get 2MB chip RAM. It works wonderfully. I would like to mount an RTC on the small PCB. What do you need for this extension? the PCB is only partially assembled. I also have this RAM expansion on the normal Amiga 500, with 2.5MB incl. Gary adapter. Here the PCB is fully populated. I just want to have a working battery on it. Is there any way to do that? I ordered this battery holder from Amigastore.eu in the hope of being able to mount it.

The parts list for RTC:

U4: OKI M6242B (I got some second hand ones from AliExpress for $2)
Y1: 32.768KHz MC306 crystal
C10: 47K-100K 0805 resistor (yes a resistor!)
C13: 100nF 0805 capacitor
C12: >=2.2uF 10V 0805 tantalum or ceramic capacitor
R1, R2, R3: 10K 0805 resistor
R4, R5: 220-470 0805 resistor
D1: BAT721C or BAT54C diode
C14,C15: 22-27pF 0805 capacitor
Battery Holder: Some cheap ebay one.

Alternatively, get a RTC-62421/72421 and you can leave off Y1, C14, C15. It makes it simpler.

[Negan]

Thank you very much! :-)

[Br0ther]

Hello friends, I am new here and eager to learn more about everything related to the A500.

Everything that has been lived in this thread is amazing, and with what intensity and enthusiasm!!, and of course with category teachers.

But even having read the 32 pages it is not clear to me if tomorrow when I connect this extension to the Trapdoor will recognize in my A500 rev. 6A (not 500 Plus) 2 MB of Chip RAM since I have installed the DKB MegAChip with AGNUS 8375 and 1 MB of Chip Mem. It has a cable that connects to Pin 36 of Gary to address the second MB of chip ($100000-$1FFFFF)

Let's see if any of you can clarify if it is possible to configure the expansion of the trapdoor along with the Gary adapter to obtain 2 MB of Chip Mem and 1'5 MB of Slow Fast, obviously putting JP7 again with the original configuration without cut, and leaving the cut in JP2 by putting the cable in the center of it.

The A500 is a 6A review, and the expansion of the trapdoor + the Gary adapter is the one sold in AmigaStore https://amigastore.eu/es/710-amiga-5...ion-rtc.html#/

My A500 rev.6a also has ...
SupraDrive 500XP (externally selectable to 2, 4, or 8 MB fast Ram) with ZuluSCSI RP2040 (SCSI to SD Card 32GB).

External selector for ROM 2.04 (37.175) or 3.2 (47.111) © 2023

Workbench 2.1 (DH0), or Workbench 3.2.2.1 (DH3).

M-TEC 68020 with autoconfig for 4MB 32BIT Fast RAM (with the possibility of switching externally to 68000 mode if desired).

Alpha-Data pass-through duplicator with Action Replay MKIII.

External Gotek with external selector to be DF0 and thus be able to keep the original Disk Drive.

A570 (CDTV) ROM 2.35 of CDTVLand (with SCSI Controller, and external selector for 2MB Fast RAM)

Amiga FM Radio in Parallel Port.

I hope that if I cannot configure it for what was said, at least can serve to keep using as 512K to continue obtaining the 2MB of Chip Mem. In my old expansion of 512K the clock has stopped working even with new battery after verifying that all PCB tracks are fine.

Excuse me if my english is not very good.

Best regards
Fran

[Nbdy]

AS I asume, if you solder the JP2 to gary, and add the gary adapter you should at least get 1.5MB of CHIP and 1.5 MB of SLOW ram ...

This is 2MB expansion so you could not get 1MB of chip and 1.5 MB of SLOW ram ...

[demolition]

Although I have not tried that specific combination yet, I do not see any reason why it would not work with 2MB chip from MegAChip + 1.5MB slow mem as long as you revert the modifications on the MB so you do not try to use 512K of that trapdoor mem as chip memory.

So effectively you would only be able to utilize 1.5MB out of the 2MB in the trapdoor expansion but that is just the way it is.

The 1.5MB of slow mem would occupy the space $C00000-$D7FFFF.

[Br0ther]

Hello, thanks to both for your answers.

I can't run the trapdoor memory correctly for 1, or 1'5MB of Slow Fast Ram. In the ATK memory test always shows this error in the first 512K C00000-C7FFFF




For 1MB Slow Ram, if I select C80000 as start address to CFFFFF, the memory test passes without problems.


For 1'5mb Slow Ram, if I select C80000 as start address to D7FFFF shows error between C80000-CFFFFF *



* It is curious as when doing the test for 1'5MB with start address in C80000 and CFFFFF as end address, the test passes without problems.



For 1'5MB also passes the test without problems between D00000 and D7FFFF.

These tests were performed with only 0'5MB of Chip RAM on board, and JP2 and JP7A as originally manufactured, that is, without cuts. And Gary Adapter JP1 and JP2 in position for 0'5MB, JP3 1MB or 1'5 according to the test to be performed, and JP4 in "More" in all cases. Sel0 and Sel1 cables in its corresponding place. There is also no cable connected to JP2.


More tests...
If JP4 is changed to position 512K the test between C00000 and C7FFFF is satisfactory.


The next test to be performed is with the cut in JP2 and the Gary adapter cable in the center of JP2, with DKB MegAChip Agnus 8375 and its cable connected to PIN 36 of Gary to Address The Second MB of Chip ($100000- $1FFFFF)...
All tests for 1'0MB or 1'5Mb of Slow Fast Mem show the same errors. And curiously if JP4 is in position for only 512K of Slow Fast Mem, I obtain according to ATK ... 2MB of Chip Mem and 0'5MB of Slow Fast Mem.
The memory tests are satisfactory for 2MB Chip Mem and 512K Slow Fast Mem.

I must also say that for this last configuration it does not matter that the Sel0 and Sel1 cables are connected or not, and the positions of JP1 and JP2 do not matter where they are.

What conclusion could you get out of all this? The truth is that I'm quite lost.

Regards

[Nbdy]

For more than 0.5MB you HAVE TO ADD the gary adapter and desolder the JP2, and solder the gary JP2 wire to the middle ...

[Br0ther]

Thanks for answering.
Sorry, I don't know if you mean something different. But previously I have commented "the next test that will be performed is with the cut in JP2 and the Gary adapter cable to the JP2 center. The DKB MegAChip Agnus 8375 has its cable connected to Pin 36 of Gary to address the second MB of Chip Ram that is on the MegAChip Board ($100000- $1FFFFF)"

All tests for 1'0MB or 1'5MB of Slow Fast Mem show on ATK exactly the same mistakes that I have put in the previous photos, even leaving the DKB MegAChip with only 512K of the Main Board of the A500.

In this way I obtain according to ATK 1MB of Chip Mem and 1'5MB of Slow Fast, but all the tests with ATK show the mistakes that are seen in the photos, except when JP4 is in 512K position. For 512K the test is OK, for 1'0 or 1'5 the tests fail.

I don't know if there is any detail that I am not seeing, or simply an A500 rev.6a with the MegAChip Board does not work as it should. Even so, as I have mentioned above, there is a combination in which the 2MB of Chip Ram are complete, and 0'5MB of Slow Fast are obtained, and all memory tests are OK.

[Nbdy]

You are mentioning slow fast ram ...

SO could you be specific is it slow or is it fast ram that is shown ...

The SLOW and the FAST rams are different rams shown by amiga ...

[Br0ther]

Do not worry, I know what is Slow Fast (Trapdoor) and Fast (expansion port on the left).

The data that I am indicating, and so the photos confirme, I am talking about addresses Slow C00000-D7FFFF.

Before buying this expansion 2MB with the Gary adapter I had a simple expansion of 512K (with clock) in the trapdoor for Slow Fast. With the appropriate modifications in JP2 and JP7A I could obtain 512K of Chip Mem in the trapdoor to complete 1MB of Chip Ram.
The MegAChip Board (Agnus 8375) is equipped with 1MB of Chip Ram, so I get a total 2MB of Chip Ram.

My old 512K expansion for the Trapdoor has begun to fail. Then I saw the possibility that acquiring this expansion of 2MB for the trapdoor together with the Gary adapter, and I thought I could obtain as previously 512K for Chip Mem and 1'5MB Slow Fast, but for some reason that I do not know this is not possible .

I previously commented that with this expansion 2MB and the Gary adapter I can get 2MB Chip Ram and 0'5MB of Slow Fast and that the memory tests with ATK were satisfactory. What I had not commented is that the tests were individual, that is, I first test the Chip Ram, and then the Slow Fast. But a few days ago I tried the "F1 option: Test All Memory", and the same failures continue to be produced. Therefore this is not trustworthy.

All tests have been performed only with the A500 rev.6A and DKB MegAChip.
M-TEC 68020, SupraDrive 500XP, and A570 were not connected at any time.

I will store this expansion of 2MB with the Gary adapter for other A500 board rev.6A. The reason not to have tested is that at some point in life the Agnus 8372 was lost.

I have managed to repair my old expansion of 512K and its clock for the trapdoor and I have installed it as previously.

In the back of this A500 I have 5 switches installed. 2 of them are to modify the configuration of the memory in the Main Board and the Trapdoor. So that...

Switch 1 Up - Switch 2 Up= 2MB Chip Mem
Switch 1 Down - Switch 2 Down= 512K Chip Mem, 512K Slow Fast
Switch 1 Up - Switch 2 Down= 1MB Chip Mem
Switch 1 Down - Switch 2 Up= 512K Chip Mem

ATK "F1:Test All Memory" is OK in all combinations.

Nbdy, thank you very much for trying to help me The installation and configuration is really simple, but this does not work well with my DKB MegAChip, and I am afraid to spoil something, so I prefer to stay with what I already had.

All the best.

[Nbdy]

But with the gary adpter you don't modify the JP7 ... just the JP2 (cut both lines and solder gary wire to middle point) ...

And on the gary adapter you have 4 jumpers for selecting setup of ram (slow - fast,1MB,0.5MB etc...)

[Br0ther]

Good attempt, but I don't forget any detail. All tests were performed reversing the cut in JP7A

In my first message I clearly explained that "obviously putting JP7 again with the original configuration without cut, and leaving the cut in JP2 by putting the cable in the center of it."

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