How to get the most memory out of an A500

[patrik]

@doctorq:

Does the eureka put its fast memory parts of the memory map mapped as reserved then? This as the Zorro2 memory space is already taken by GVP memory and the Zorro2 IO space aint big enough to hold 3.5MB. A showconfig output from that computer would very interesting . Btw, does it require any software to map some parts of its memory into the system free memory list?


/Patrik

[patrik]

@SilvrDrgn:

Your CTX-monitor will probably get a seriously reduced life-length with all the heat building up inside it when its top ventilation is covered by that printer.

(edit):

Looked at the pictures and read about your A500 with an A2091 inside a Dataflyer 500 case using its Zorro2-to-86-pin-A500-expansion adapter. You also mentioned there that the A2091 card disappears when you reset the A500 so it sounds like the A2091 doesn't reset if the A500 resets. A Zorro2 card needs to be reset to respond to "autoconfiguration-requests", which would explain the behaviour you are experiencing.

When looking at this picture - the internals of a Dataflyer 1000 (identical to DataFlyer 500 internals according to The Big Book of Amiga Hardware), the Zorro2-to-86-pin-A500-expansion adapter looks like it is a straight-forward connection between pin 1-86 of the two connectors and pin 87-100 on the Zorro2 connector are just left unconnected.

One of the signals that the A2091 wont be getting then is the /BUSRST signal (Zorro2 pin 94). The /BUSRST signal is a output only (to the Zorro2 card) buffered version of the /RST signal (Zorro2 pin 53 and 86-pin A500 expansion pin 53) and is the signal a Zorro2 card that is not able to reset the machine should use for knowing when to be reset.

As the A2091 is a Zorro2 card not able to reset the machine it should use the /BUSRST signal if it follows the Zorro2 specification and would then not be able to reset on your setup.

This picture of the A2091 from the front shows that /BUSRST is connected and this picture of the A2091 from the back shows that /RST is not connected (pictures courtesy of The Amiga Hardware Database) - thus can the A2091 only be reset with the /BUSRST signal which confirms that it will not be able to reset on your system.

As this is a one-slot Zorro2 solution, you should be able solve this issue by a quick hack and just connect /RST to /BUSRST - in other words connect pin 53 of the 86-pin connector to pin 94 of the 100-pin Zorro2 connector on the Dataflyer Zorro2-to-86-pin-A500-expansion adapter you are using.

If you want to do it according to the book - which in this case has to be the A2000 schematics, you need one 74LS08 quad AND gate and one 1kOhm resistor. Actually you only need to use two of the four AND gates in the 74LS08.

To the first gate you should connect /RST as one input and +5V as the other input. To the second gate you should connect the output of the first gate plus one end of the 1kOhm resistor and +5V as the other input. The end of the resistor not connected to the second gates input should be connected to +5V which will make the resistor act as a pullup-resistor. The output of the second gate is then your /BUSRST, made according to the book .

A simple schematics of it should look something like this:

Code: [Select]

                         ____
        ____       +5V --|    \
 +5V --|    \            |AND  |---- /BUSRST
       |AND  |---+-------|____/
/RST --|____/    |
                 R
                 |
                +5V
You ofcourse also need to connect Vcc (pin 14) and GND (pin 7) of the 74LS08 to +5V and GND from the 86-pin connector and the spare AND input pins of the 74LS08 should be connected to GND.

An example arrangement seen from the 74LS08 would be this:

Code: [Select]

74LS08 pin:    Connected to:                             Comment:
1              86-pin Connector pin 5                    +5V
2              86-pin Connector pin 53                   /RST
3              74LS08 pin 5 + pullup side of resistor    To second gate
4              86-pin Connector pin 5                    +5V
5              74LS08 pin 3 + pullup side of resistor    From first gate
6              Zorro2 Connector pin 94                   /BUSRST
7              86-pin Connector pin 1                    GND
8              Nothing                                   None
9              86-pin Connector pin 1                    GND
10             86-pin Connector pin 1                    GND
11             Nothing                                   None
12             86-pin Connector pin 1                    GND
13             86-pin Connector pin 1                    GND
14             86-pin Connector pin 5                    +5VI have double-checked this, but do check it by yourself to make sure it is ok. I would anyhow suggest that you try the /RST to /BUSRST quick hack solution mentioned above first.

References:
Part 1 of 6 of the A500/2000 Technical Reference Manual - page 80, 84-86, 92 and 98-100 is of special interest.
Part 6 of 6 of the A500/2000 Technical Reference Manual - page B2000-10a is of special interest.
74LS08 Datasheet


/Patrik

[patrik]

@SilvrDrgn:

(edit):

Checked through the circuit today once more today and found that I had missed one thing. The A2000 also has a 1kOhm pullup-resistor after the second gate, so for it to be correct, it should look like this:

Code: [Select]

                         ____
        ____       +5V --|    \
 +5V --|    \            |AND  |---+----- /BUSRST
       |AND  |---+-------|____/    |
/RST --|____/    |                 R
                 R                 |
                 |                +5V
                +5VCorrected example arrangement seen from the 74LS08:

Code: [Select]

74LS08 pin:    Connected to:                                               Comment:
1              86-pin Connector pin 5                                      +5V
2              86-pin Connector pin 53                                     /RST
3              74LS08 pin 5 + pullup side of first resistor                To second gate
4              86-pin Connector pin 5                                      +5V
5              74LS08 pin 3 + pullup side of first resistor                From first gate
6              Zorro2 Connector pin 94 + pullup side of second resistor    /BUSRST
7              86-pin Connector pin 1                                      GND
8              Nothing                                                     None
9              86-pin Connector pin 1                                      GND
10             86-pin Connector pin 1                                      GND
11             Nothing                                                     None
12             86-pin Connector pin 1                                      GND
13             86-pin Connector pin 1                                      GND
14             86-pin Connector pin 5                                      +5VWhen looking at this schematic, it actually looks a bit silly - two exactly similar gates in a chain with exactly the same output pullup. Nevertheless, this is exactly how it is done in the A2000, but with some differences. First of all, the output from the first gate doesn't only drive the input of the second gate in the A2000, it is also used as a buffered reset-signal (/BRST), connected directly to several circuits on the motherboard. Secondly using the second gate for the buffered Zorro2 reset-signal /BUSRST in the A2000 separates the motherboards buffered reset-signal /BRST from the Zorro2 bus reset-signal /BUSRST. But in this case, as there will be nothing using the output of the first gate except the input of the second gate, there is no need for using two gates, alas a very sensible idea would be to remove one of the gates and do it like this instead:

Code: [Select]

       ____
 +5V --|    \
       |AND  |---+----- /BUSRST
/RST --|____/    |
                 R
                 |
                +5VExample arrangement for the above schematics seen from the 74LS08:

Code: [Select]

74LS08 pin:    Connected to:                                               Comment:
1              86-pin Connector pin 5                                      +5V
2              86-pin Connector pin 53                                     /RST
3              Zorro2 Connector pin 94 + pullup side of second resistor    /BUSRST
4              86-pin Connector pin 1                                      GND
5              86-pin Connector pin 1                                      GND
6              Nothing                                                     None
7              86-pin Connector pin 1                                      GND
8              Nothing                                                     None
9              86-pin Connector pin 1                                      GND
10             86-pin Connector pin 1                                      GND
11             Nothing                                                     None
12             86-pin Connector pin 1                                      GND
13             86-pin Connector pin 1                                      GND
14             86-pin Connector pin 5                                      +5VEven if I have said it atleast two times(?) already, I recommend you to try the quick hack solution first as it only requires short wire . Good luck!

@doctorq:

Then except from the 512kB chip, it should add 1.8MB ranger RAM - from ranger RAM start at 0x00C00000 to just before the beginning of the real time clock space at 0x00DC0000 which equals to 1.8MB. That would correspond nicely with how much fast you remember it used to have at power up. If you remember to check it next time you go home, it would be very interesting to know how it maps the memory :=).

@Kronos:

With a gary-adapter as the Eureka has, it is possible to have up to 1.8MB ranger RAM, right?


/Patrik