Started by Shining, 00:45, 13 January 15
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Quote from: Audronic on 13:33, 09 January 19The voltages at rest should be :-IC206 74LS38. Is it a 74LS38 ?Using a CRO or VoltMeterPins 9 and 10 + 4.1 Volts. Pin 8 + 0.2 VoltsPins 4 and 5 + 0.2 Volts. Pin 6 + 4.8 VoltsMonitor Pin 6 ONLY and do a Cat it should at some stage toggle LOW to + 0.2 Volts.If not then Monitor pin 8 and repeat the test. It should go from + 0.2 Volts to +4.8 Volts.Any of the above don't change then :- Change the IC206
Quote from: Bryce on 14:00, 09 January 19It could still be IC206. There's a difference between a signal going high/low on a scope and actually being able to drive a gate it's connected to. I'd change IC206 anyway before looking further.
QuoteAfter reset has been sent to the µPD765A/µPD765, the unit select Lines US0 and US1 will automatically go into a polling mode. In between commands (and between step pulses in the seek command) the µPD765A/µPD765 polls all four FDDs looking for a change in the Ready Line from any of the drives. If the Ready line changes state (usually due to a door opening or closing) then the µPD765A/µPD765 will generate an interrupt. When Status Register 0 (ST0) is read (after Sense Interrupt Status is issued), Not Ready (NR) will be indicated. The polling of the Ready line by the µPD765A/µPD765 continues continously between commands thus notifying tthe processor which drives are on or off line. Each drive is polled every 1.024ms except during the Read/Write commands. When used with a 4MHz clock for interfacing to minifloppies, the polling rate is 2.048ms.
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