Hello Forum Chaps & Chapettes
Having a few hours to spare today, I decided to finally Hack an A500 that I had picked up from a boot sale a few months ago.
This A500 was planned to be the testbed of all sorts of hackery regarding Memory addition to the trapdoor slot & some CPU speed up.
For the moment I wanted to get her ready for the above therefore carried out the following..
1) On Board 1MB ChipRAM, thus leaving the trapdoor free, Zetr0 kindly sent me some RAM chips a while ago for this, sadly one of the chips was faulty so I used the chips from a spare A501 which had socketed chips.
This was quite a straight forward mod, simply setting the 2 Jumpers on the Mobo for 1MB chip, vacating all the PCB holes of solder and then fitting the RAM, still need to find some suitable decoupling capacitors but it all works fine.
2) Dual Kickstart (3.1 / 1.3), 3.1 needed for operation with the HD+8 SCSI FASTRAM unit I have, and 1.3 for standalone gaming.
Being short of cash & not really seeing the point of all those fancy kickstart switchers I programmed a 27C800 (1MB) eprom as follows.
KS1.3 256K + KS1.3 256K + KS3.1 / V40.63 512K.
These Eproms are 42 Pin DIL unlike 27C400 (512K) which are 40 Pin DIL, of course the Mobo has a 40 Pin DIL socket meaning the top 2 legs will overhang the socket which is fine as one of these is not used & the other is A18 which will be used to toggle the Hi or Lo 512K of the Eprom.
A18 is set to 0V-GND for the Lo (KS3.1) or to +5V via a 4k7 pull up resistor for the Hi (KS1.3) mode of operation.
The 4k7 resistor is a must to protect the miggy from any shorts that may ocour or should the switch fail at some point.
This part of the Hack unfortunately needed a little more work as the A500 did not like the 27C800, Commodore in their wisdom have included PCB locations for 68000 Address line pull up resistors, but in their penny pinching ways did not populate them.
Having no 4k7 SIL packs to hand, I fashioned some homemade versions as can be seen in the piccies.
RP106 & RP107 provide pullup facilities for Address lines A1 to A16 which is sufficient for the kickstart....
And.... It all works absolutely fine.
Just need to find some time to get on with the trapdoor / Gary hack I have in mind...:shhh:
Enjoy the piccies
TC
Having a few hours to spare today, I decided to finally Hack an A500 that I had picked up from a boot sale a few months ago.
This A500 was planned to be the testbed of all sorts of hackery regarding Memory addition to the trapdoor slot & some CPU speed up.
For the moment I wanted to get her ready for the above therefore carried out the following..
1) On Board 1MB ChipRAM, thus leaving the trapdoor free, Zetr0 kindly sent me some RAM chips a while ago for this, sadly one of the chips was faulty so I used the chips from a spare A501 which had socketed chips.
This was quite a straight forward mod, simply setting the 2 Jumpers on the Mobo for 1MB chip, vacating all the PCB holes of solder and then fitting the RAM, still need to find some suitable decoupling capacitors but it all works fine.
2) Dual Kickstart (3.1 / 1.3), 3.1 needed for operation with the HD+8 SCSI FASTRAM unit I have, and 1.3 for standalone gaming.
Being short of cash & not really seeing the point of all those fancy kickstart switchers I programmed a 27C800 (1MB) eprom as follows.
KS1.3 256K + KS1.3 256K + KS3.1 / V40.63 512K.
These Eproms are 42 Pin DIL unlike 27C400 (512K) which are 40 Pin DIL, of course the Mobo has a 40 Pin DIL socket meaning the top 2 legs will overhang the socket which is fine as one of these is not used & the other is A18 which will be used to toggle the Hi or Lo 512K of the Eprom.
A18 is set to 0V-GND for the Lo (KS3.1) or to +5V via a 4k7 pull up resistor for the Hi (KS1.3) mode of operation.
The 4k7 resistor is a must to protect the miggy from any shorts that may ocour or should the switch fail at some point.
This part of the Hack unfortunately needed a little more work as the A500 did not like the 27C800, Commodore in their wisdom have included PCB locations for 68000 Address line pull up resistors, but in their penny pinching ways did not populate them.
Having no 4k7 SIL packs to hand, I fashioned some homemade versions as can be seen in the piccies.
RP106 & RP107 provide pullup facilities for Address lines A1 to A16 which is sufficient for the kickstart....
And.... It all works absolutely fine.
Just need to find some time to get on with the trapdoor / Gary hack I have in mind...:shhh:
Enjoy the piccies
TC
