On 1/4/02 at 4:22 PM Dexter wrote: >I'm still looking for a schematic of the QL PCB. Also, the 8049 details.
Actually, you do not need the 8049. All it does can be done using a different device and handling the difference on the software side (translation: modified OS code). >I'm thinking of prototyping a 680X0 board with the basic QL facilities, >minus the dodgy serial and net ports, plus IDE. I have a strongarm design >here which has USB and ethernet and I'm seeing if there's a way to take >advantage of any of that knowledge. A quick question: what do you use for USB? >Also, the +5v is obvious, but if you ignore the net, serial and microdrive >interfaces, was the +/-12v used anywhere else? Only as a bug fix for the 8302 ULA which incorporates the 9049 IPC interface, microdrive logic, reset, half the serial ports and the network, all of which you can forget - except for the RTC. The later is a simple 32 bit second sounter. If you don't use a 8302, then you don't need +-12V. Serial port levels can easily be handled by something like a MAX232 or it's many successors and clones. >Finally, on some QLs there was a variable capacitor (?) mid-board. What >did it do? How was it set? It disappeared on later revision boards. It was used in the RTC oscillator (32768Hz crystal plus a few other components). The purpose of the variable cap was to adjust the exact frequency. However, the osc. circuit used in the ULA does not lend itself to precision, and the select logic for the 8302 has a bug which more often than not corrupts the RTC register when power is applied. With later board revisions, any pretense at battery back-up for the RTC internal to the 8302 was abandoned, and with it the need for the RTC to be very precise - it was enough that the drift was not too bad within a single session (between two power-ups). Later, the GC and SGC boards introduced their own RTC which operates by loading the contents of the local RTC into the 8302 RTC, where it can then be compatibly read. I am really very intrigued at what you propose to design - especially since I am myself involved in an (ever ongoing!) process of designing a QL board to replace the GC/SGC. Even so, it seems there is a real need for something that would be a true replacement of a SGC, rather than it's successor, something like a SGC II. The demise of the SGC is connected to an Altera EP18010 being used for all theglue logic, a chip which has long ago been obsoleted. The FDC controller on the SGC is also not available any more, but it has a fully compatible replacement (made by SMSC). Also, the current state of affairs with memory, would make a potential 68EC020 based board for the QL very tiny - 16M of RAM could easily be squeezed into two SDRAM chips - and that only because 16-bit wide ones are easyer to get then the 32-bit wide ones. Something along these lines would make a great QL based SBC. Not one to contend for the fastest QL out there, but it should be very practical. Nasta
