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MCU mode type A

The OSP32 board has an on-board SAID. This SAID is connected to the MCU. They communicate using physical layer MCU mode type B also known as two-wire SPI.

This document explains how to reconfigure the OSP32 board to use MCU mode type A also known as one-wire Manchester. This is the physical layer the RGBI chips use. It is also the default mode of the SAIDs. The SAID OUT on the OSP32 board has a bit burned in its OTP to use type B instead.

You need an OSP32 board V11 or higher to be able to reconfigure as described here.

Example OSP_aospi/examples/aospi_mcua uses the reconfiguration described in this documentation.

Schematics

On the OSP32 board, the MCU (an ESP32) has its internal SPI block wired, via a level shifter, to (SIO1 of) SAID OUT. SIO2 of SAID OUT is exposed on the ERNI connector labeled OUT. This is the start of the OSP chain.

The SAID OUT on the OSP32 board has a bit (SPI_mode) burned in its OTP to use type B communication, instead of the default type A communication. This cannot be changed (OTP burn is forever). In order to use type A communication, we need to bypass SAID OUT, and either connect an RGBI or a SAID without the SPI_mode bit burned to 1.

The OSP32 board, v11 and higher, has jumpers to wire the bypass. The schematics below show the jumpers. By default they route the N and P line from the MCU (level shifter) to SAID. When the jumpers are removed the N and P line are interrupted, and another OPS node can be connected. To make this easier, the jumpers have a 5V and a GND next to it.

OPS32 schematic

Reconfigure

Physically, the jumpers are on the backside of the OSP32 board, below SAID OUT. The photo on the right shows the N and P jumper present, the default configuration. The middle photo shows the two jumpers removed. We have now four pins exposed: 5, N, P, G; this is precisely what an ERNI cable carries. The photo on the right shows a patched ERNI cable being plugged into those four pins.

Reconfigure steps

New connection

We made the cable by cutting a standard ERNI cable and soldering four female jumper connectors. The other side, the ERNI connectors can then be plugged in, for example, the RGBI strip, the SAIDbasic board or the SAIDlooker board.

Cable

As an alternative we made an ERNI breakout board: a small PCB converting from 4 pin female header to an ERNI connector.

New connector

Pull-up

The OSP32 has a pull-up on the P line (see schematics at the start of this document). It would have maybe been better if this pull-up were on the SAID side of the jumpers, but it is on the MCU side. This means that even with the jumpers removed, the P line is pulled up.

This has the advantage that if you plug in a SAID or an RGBI it is configured for MCU mode automatically.

If you want to do an experiment with USE mode, you have to add a pull-up on N as well. If you would want EOL or LVDS mode, you would have to remove the R.

Match

There must be a match between the hardware and software.

  • When using SAID OUT (no bypass), the software must configure aospi for type B (aospi_phy_mcub), because the SAID OUT is configured for that (a bit permanently burned in its OTP).

  • When bypassing the SAID OUT and connecting another head node, we need to know which physical layer that head node uses.

    • If the new head node is an RGBI (E3731I), software must use type A (aospi_phy_mcua) because that is the only protocol implemented by RGBI (in its controller).

    • If the new head node is a SAID (AS1163), there are two options. Either the SAID has the OTP bit SPI_mode clear (default), in which case software must use type A (aospi_phy_mcua). If the OTP bit SPI_mode is set, software must use type B (aospi_phy_mcub).

WARNING on type A: When using as head node an RGBI or a SAID v1.0 there is an issue. Those nodes generates one extra clock transition in their response telegrams in bidir mode. The aospi library can not handle that extra transition. Therefore aospi supports physical layer type A for RGBI and SAID v1.0 in loop mode but not in bidir. SAID v1.1 does not generate the extra clock transition; aospi supports v1.1 in loop as well as in bidir.

Type A (1-wire Manchester) Loop BiDir
RGBI yes not in aospi
SAID v1.0 yes not in aospi
SAID v1.1 yes yes
Type B (2-wire SPI) Loop BiDir
RGBI not in hw not in hw
SAID v1.0 yes yes
SAID v1.1 yes yes

See saidversions for finding out which SAID version is on a board.

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