I'm stuck and need help. The data sheet is vague about issues like whether to ensure the TMS3705 is out of sleep mode, and the timing diagrams in the datasheets don't address this - but one timing diagram in the instructional manual (but not the datasheet!) shows the TMS3705 being blipped with a zero for Twake on TXCT Tinit (2.05 msec) before starting the write.
In any event I cannot get the TMS3705 to enter synchronous data transfer mode. I need to know what mistake I'm making.
To turn on synchronous mode but leave the chip otherwise in the default state, I:
- Start with TXCT high
- Set TXCT low for Twake (50 µsec according to the instructional pdf, but not mentioned in the datasheet)
- Set TXCT high for Tinit (3 msec) to allow the TMS3705 to wake up
- Set TXCT low for 128 µsec (Tmcr) for the first, zero, bit,
- Set TXCT high for 5*Tmcr = 640 µsec (auto division factor = 1111 and synchronous mode = 1)
- Set TXCT low for 2*Tmcr, followed by keeping TXCT low for 50 msec (charge period)
- Set TXCT high and wait for SCIO to go high.
If I do this, SCIO behaves exactly as it does during asynchronous transfer mode.
Here you can see the problem. You can see the wakeup pulse on TXCT followed by the zero bit, then the charge period of 50 msec. SCIO does not go high and wait for clock pulses from TXCT after the charge period (In the above shot, toggling TXCT is triggered if SCIO goes high within Tr + 1 msec, so in this case TXCT simply stays high because SCIO doesn't signal that data are ready.) No matter what I do with TXCT, SCIO stays in asynch mode! Even if I try forcing the issue by pulsing TXCT, TXCT is ignored:
This is driving me crazy. I would be most grateful for any help you can give.