How to get the most memory out of an A500

[Kronos]

rayt wrote:
You could add a zorro2 board(if you find one) with an a2000 expansion slot and add a blizzard2060 with 256MB ram :-D

And how do you do that ?? (hint the 2060 has 4 slots with each 32MB max).

On topic:
Without 030/40/60-card:
2MB chip
1.3MB "ranger"
8MB fast

[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