Apple LocalTalk interface box

[Shinobi Kenobi]

Good news, works fine between the new LC475 and the Performa 5300.
Now I have working system to measure on with the logic analyzer.

My first ideas :
- it's slow to todays standards, but for the 90 with only small files and minimal extra HW needed I would have loved it.
- Also the slave computer gets slower, even on the LC475.

My original plan was to use the external clock option (or patch the mainboard clock to the 85C30) to increate the speed x3 or x4,
but this will probably only increase the load on the CPU, making the system even slower ?
AppleTalk was cheap, but without any ram buffer nor DMA support, it needs the CPU to often to intervene.

Just within the past day or two, I came across an extension or some software that allowed DMA transfers for AppleTalk. But now after reading your post, I don't remember where it was I found it.

 

[joevt]

My first ideas :
- it's slow to todays standards, but for the 90 with only small files and minimal extra HW needed I would have loved it.
- Also the slave computer gets slower, even on the LC475.

My original plan was to use the external clock option (or patch the mainboard clock to the 85C30) to increate the speed x3 or x4,
but this will probably only increase the load on the CPU, making the system even slower ?
AppleTalk was cheap, but without any ram buffer nor DMA support, it needs the CPU to often to intervene.

External clock is probably the easiest and best choice:
https://68kmla.org/bb/threads/localtalk-but-faster.45615/post-505309

The PCLK could be used, but there's a couple issues with that:
- Different Macs have different PCLKs. Maybe only Power Macs had PCLKs in the >10MHz range.
- The PCLK has to go through the baud rate generator which reduces the maximum bit rate by a lot. You would need > 4 * 3.678 MHz to exceed the 230.4 kbps option allowed by using the 3.678 MHz from the RTxC pin.

The external clock can easily do 1 Mbps because both machines will use the same clock and therefore can use the X1 Clock Mode instead of X16 or X32.

It might be interesting to see if you can output the transmit clock TRxC to one of the pins (HSKi?). Then one Mac can be the source of the external clock and they can use X1 mode. It would require special cables.