387 SENT Receiver with SPI Interface
387 : SENT Receiver with SPI Interface
- Author: Philipp Kraft
- Description: Configurable SENT receiver with SPI slave interface
- GitHub repository
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- Clock: 40000000 Hz
How it works
The chip receives a SENT signal on ui[0] and decodes it into a 32-bit frame, checked against
its SAE J2716 CRC-4. The decoded frame and a config register are available over an SPI slave
interface on the bidirectional pins: CS (uio[0]), MOSI (uio[1]), MISO (uio[2]) and SCK
(uio[3]).
Every SPI transaction is an 8-bit command byte (bit 7 = write, bits 6:0 = register address), MSB first, followed by a 32-bit data word MSB first (shifted out on a read, or in on a write):
| Address | Register | Access | Contents |
|---|---|---|---|
0x00 |
frame_data |
RO | the latest good decoded frame |
0x01 |
config |
RW | bit [4]: CRC check enabled (default on); bit [3]: pause pulse present after the CRC nibble (default off); bits [2:0]: data-nibble count, 1-6 (default 6) |
0x02 |
status |
RO | bit [1]: data_error; bit [0]: data_valid (same as uo[1:0], see below) |
Writes to config outside the 1-6 nibble-count range are ignored; every other bit is written as
given. Since a write replaces the whole register, always send the full desired value, not just
the bit you're changing. Writing config mid-frame doesn't disturb a frame already being
received; the new settings take effect on the next one.
uo[0] (data_valid) is set once at least one frame has been decoded successfully since reset.
uo[1] (data_error) is set when the most recent frame attempt failed - a bad CRC, an
out-of-spec pulse length, or a watchdog timeout waiting on the sensor - and clears again on the
next good frame. Both bits are also readable over SPI at status for a master with no free GPIO
to watch them on directly.
How to test
Drive a SENT signal into ui[0]. Once a full frame has been received (uo[0] goes high), pull
uio[0] (CS) low, clock out the command byte 0x00 (read frame_data) on uio[1] (MOSI), then
clock 32 more times to shift the decoded frame out on uio[2] (MISO), MSB first.
External hardware
A SENT sensor connected to ui[0], and an SPI master to read out the decoded data.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | sent_in | data_valid | SPI CS |
| 1 | data_error | SPI MOSI | |
| 2 | SPI MISO | ||
| 3 | SPI SCK | ||
| 4 | |||
| 5 | |||
| 6 | |||
| 7 |