Datasheet

Jon Waddington
24
3.4.3 CM12 Protocol
The serial communications protocol for the CM12 states that the baud rate is 4800 bits
per second (bps). There is a start bit, a stop bit and no parity bit.
Figure 3.4.3.1, below shows how the serial communication protocol between the
Propeller and the CM12 looks. The transmission is in two parts; the first part addresses
the device and the second part sends the function to be performed.
The first byte to be sent is the Header. The structure of the Header is shown in the table
below. The upper 5 bits define the amount to dim the device. Bit 2 ensures that the
CM12 stays synchronized by being set to ‘1’. Bit 1 defines whether the following byte will
be the address (0) of the device or a function (1) and bit 0 defines whether the following
byte will be an extended transmission (1) or a standard transmission (0 ) [32]. For the
purpose of the Information systems, extended transmissions were not applicable.
The number of dims is a value between 0 and 22 where 22 is equivalent to 100% and 0
is 0% so a value of 11 would half the brightness of the light. Only specified lamp
modules can be dimmed.
The next byte holds the address of the device or the function. The 4 most significant bits
Figure 3.4.3.1. A Standard Transmission between the Propeller and the CM12
Header
7
6
5
4
3
2
1
0
Number of Dims
1
F/A
E/S