Other Parts Discussed in Thread: LMX2492, LMX2491
I'm having difficulty with read back from the LMX2492-Q1. Unfortunately the data sheet is less than clear as to how read back should be performed via the micro wire interface. I am not using code loader though I have compared my register settings with those generated by the code loader software. Write functionality was succesfully verified by sending a single byte to Register 2 (0x0 0x2) to enable/disable the chip and a ~40 mA change in power consumption was observed. I was able to toggle the enable/disable function with both a register setting and by using the CE line.
The following bytes were transmitted to the LMX2492 in an attempt to enable read back on the MUXout line:
0x0 0x27 0x3A [Register 39, MUXout_MUX = readback, MUXout_PIN = Output Push-Pull]
I then attempted to read back a register using a variety of methods. I've probed the MUXout line during the various attempts and it is always pulled to ground.
It would seem the correct method is to transmit a read bit on the MSB of the first address byte. Per a post dating form 2015 the R/W = 1 for READ and R/W = 0 for WRITE.
Pull LE line low
0x80 0x2 0x0 [R/W = 1, Register 2, dummy payload of 0x0]
Pull LE line high
Returns 0x0 regardless of register setting. I've probed the MUX output trace and it is held to ground during read back. I've also tried reading other registers including those with a POR != 0x0.
As a second check I programmed MOD_PIN to Output Push-Pull and MOD_MUX to R Divider/4. I confirmed a 100-MHz 0.5-Vpp input at the OSC terminal between the power divider and AC coupling capacitor. There was no output signal on the MOD line, which was also pulled to ground. All VCC pins measured 3.3V and the VCP pin is at 5.0V.
I'm at a loss at the moment. Any help would be greatly appreciated.
Thanks,
David
