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Reverse engineering and control of an old flip dot display with Brose VM-IIC controller

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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.

Transceiver schematic

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Reverse engineering and control of an old flip dot display with Brose VM-IIC controller

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