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Being able to decode scope captures are pretty useful when debugging. Linear Technology has an isoSPI Analyzer board (LTC DC1907A) which automatically converts the isoSPI signal into 4-wire SPI for use with the LTC6804, but we can do the same thing manually using an oscilloscope.
Scope Settings
| Probe between | isoSPI positive and negative |
|---|---|
Logical Signals
(Taken from Table 1 in the LTC6820 datasheet)
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| SPI Master Event | Transmitted Pulse |
|---|---|
| CS Rising | Long +1 |
| CS Falling | Long –1 |
| SCK Latching Edge, MOSI = 1 | Short +1 |
| SCK Latching Edge, MOSI = 0 | Short –1 |
(Taken from Table 3 in the LTC6820 datasheet)
| Received Pulse | SPI Port Action | Return Pulse |
|---|---|---|
| Long +1 | Drive CS high | None |
| Long -1 | Drive CS low | Short -1 pulse if MISO = 0 No return pulse if MISO = 1 |
| Short +1 |
| |
| Short -1 |
|
Example 1: Logical High (0xFF)
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When debugging the LTC6804 and the LTC2484 for MSXII, we ran into a few issues. Here are a couple things to watch out for:
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