Brose 22-044-502-020 with VM-IIC controller

I recently got hold of a Brose flipdot display. Naturally I wanted to find out how it works and how to drive it. My efforts of understanding it will be documented in this repo.

The Alcatel MT 1028 I ICs seem to be a Brose clone of the FP2800A flipdot drivers.

Protocol

The Brose Vollmatrix Control with VM-IIC controller has quite a cursed hardware layer.

It uses two RS422 transceivers to transmit the SDA and SCL signal of an I²C bus to all connected displays. Because this method of transmission is inherently unidirictional, it means that you somehow have to ignore the missing ACK from the I²C slaves.

3 bytes are sent via the bus to update 3 PCF8574 I²C port expanders. Connected to those are two FP2800 row drivers located on the VM-IIC controller card and level shifters for signals on the 60 pin header. Those signals are for the FP2800 column drivers and their module select enable signal located on the flipdot modules. The mapping for the port expanders is listed below.

For the correct method of controlling the FP2800 flipdot drivers, look into its datasheet or at my implementation. Maybe I'll go into more depth in the future™.

Schematic

I reverse engineered the most important aspects of the VM-IIC and documented it here.

CPC Plug Pinout

Pin	Color	Function
1	White	SDA A
2	Brown	SDA B
3	Green	SCL A
4	Yellow	SCL B

Pluggable Screw Terminal on VM-IIC Board

Pin	Color	Function
1	Red	24V
2	Blue	GND
3	White	SDA A
4	Brown	SDA B
5	Green	SCL A
6	Yellow	SCL B

I²C Port Expander Mapping

Address	I²C Bit	Function
0x40	0	Module Select 8
	1	Module Select 7
	2	Module Select 6
	3	Module Select 5
	4	Module Select 4
	5	Module Select 3
	6	Module Select 2
	7	Module Select 1
0x42	0	N/C
	1	Column FP2800 B1
	2	Column FP2800 B0
	3	Column FP2800 A2
	4	Column FP2800 A1
	5	Column FP2800 A0
	6	Column FP2800 DATA
	7	Row FP2800 A2
0x44	0	Row FP2800 A1
	1	Row FP2800 A0
	2	Row FP2800 B1
	3	Row FP2800 B0
	4	Row FP2800 Low DATA
	5	Row FP2800 Low ENABLE
	6	Row FP2800 High DATA
	7	Row FP2800 High ENABLE

Row Low: 1-14
Row High: 15-20

Row Drivers

The VM-IIC board has eight "module select" outputs and uses two FP2800 ICs to control matrix rows. IC1 drives the rows 1 to 14, IC13 controls rows 15-20. That means one VM-IIC board can control up to 8 flipdot panels, each having up to 28x20 pixels.

Matrix	FP2800	Signal
SET 1	IC1	0A
SET 2	IC1	0B
SET 3	IC1	0C
SET 4	IC1	0D
SET 5	IC1	0E
SET 6	IC1	0F
SET 7	IC1	0G
SET 8	IC1	2A
SET 9	IC1	2B
SET10	IC1	2C
SET11	IC1	2D
SET12	IC1	2E
SET13	IC1	2F
SET14	IC1	2G
SET15	IC13	0A
SET16	IC13	0B
SET17	IC13	0C
SET18	IC13	0D
SET19	IC13	0E
SET20	IC13	0F
RESET 1	IC1	1A
RESET 2	IC1	1B
RESET 3	IC1	1C
RESET 4	IC1	1D
RESET 5	IC1	1E
RESET 6	IC1	1F
RESET 7	IC1	1G
RESET 8	IC1	3A
RESET 9	IC1	3B
RESET10	IC1	3C
RESET11	IC1	3D
RESET12	IC1	3E
RESET13	IC1	3F
RESET14	IC1	3G
RESET15	IC13	1A
RESET16	IC13	1B
RESET17	IC13	1C
RESET18	IC13	1D
RESET19	IC13	1E
RESET20	IC13	1F

RS422 interface

Many hobby projects use microcontrollers like Arduino or ESP2866/ESP32 to control devices. To translate TTL level I²C signals to RS422 you can use for example MAX485 transceiver chips.