SE/30 Real Time Clock Chip

[bdurbrow]

I'm absolutely positive that this has been posted before; but both the site search and google are not turning it up.

Somebody had extracted or reverse engineered the code for the SE/30's RTC, and posted it somewhere.

Anybody remember where???

 

[cheesestraws]

Someone built a replacement PRAM chip based on a little Atmel chip, is that what you're thinking of?

https://www.reddit.com/r/VintageApple/comments/91e5cf

 

[bdurbrow]

I was pretty sure it was a PIC that their code ran on, but if it's got the requisite protocol laid out, I could start from there and cook up something suitable...

 

[cheesestraws]

Hmmmm, I don't think I've heard about a PIC one if so, only an AVR. Are you thinking of the ADB chip? That's a PIC on the original boards, and the code for that is definitely floating about.

 

[robin-fo]

Did anybody have success with making one? I got the code from here and compiled it with make and avr-gcc. As I don't have a special avr programmer, I loaded Arduino ISP on a Arduino Micro and connected it to the Attiny. Using avrdude -v -P /dev/cu.usbmodem1101 -p attiny85 -c avrisp -b 19200 -U flash:w:/somepath/MacPlusRTC.axf I was able to successfully flash it to the Attiny. However, it doesn't appear to work now as I cannot measure the 1Hz pulse and I can also flash it again which shouldn't be the the case if the reset pin was successfully disabled.

 

[robin-fo]

Update: I was able to get a 1Hz clock using another Attiny and by appending -U lfuse:w:0xE2:m -U hfuse:w:0x5F:m -U efuse:w:0xFF:m to the avrdude command. However, my SE/30 still refuses to boot with this RTC chip. The curious thing is that it boots fine using a RTC chip from a Macintosh Classic...

 

[pgreenland]

@robin-fo Did you get this working on your SE/30 in the end? I've got a few battery bombed ones which I'd like to swap out the RTC on.

 

[robin-fo]

Nope.. I think it the RTC in the SE/30 is clocked faster than in the SE. I had to order a NOS part.

 

[pgreenland]

Ahh that would make sense.....I've been trying to build my own based on the few examples I found online.

One of them mentioned a max serial clock of 20Khz...I'm seeing closer to 250Khz. Thanks for backing up my suspicion that the clock rate was increased.

I failed to do the basic maths or how long have I got between clock edges....about 24 instructions at 8Mhz. I may need to write some assembly .