Medlab medizinische Diagnosegeräte GmbH EG01010 User Manual
Version 1.06
16
Serial Transmission Protocol 2
The board can transmit a single ECG waveform and optionally a respiration waveform synchronously,
a pulse value, a respiration value (if the optional respiration board is fitted to the base ECG board) and
several status bytes. Transmission is done in blocks. The integrity of the blocks is secured by:
1) an even parity bit in each transmitted byte.
2) a checksum for each block
Even parity in this case means that the sum of all bits in one byte, including the parity bit, is „0“.
The module can receive commands over its serial interface. For example, the user can select transmissi-
on speed of the wave block, set the amplification of the ECG amplifiers and select which channels should
be transmitted by the board. The transmitted channels that are available with a three lead cable are:
1) I, Einthoven Lead or
2) II, Einthoven Lead or
3) III, Einthoven Lead
4) Respiration curve (optional respiration board needed)
To reduce overhead for the waveform transmission, the wave block uses another checksum algorithm as
the status and value blocks do.
The EG01010 works with a three lead cable.
The board contains a lead-off detection that gives information about a non-connected electrode.
Transmission is done in blocks. The basic interface parameters are:
115200 baud, 1 start bit, 8 data bits, an even parity bit and one stop bit.
The first block transmitted will be a status block.
The default settings after power up are:
100 wave blocks per second, II activated, 1cm/mV amplification, monitoring bandwidth, 50 Hz filter active.
The host can adjust this to his needs by sending commands to the module.
To keep the traffic on the serial line as low as possible, the following protocol has been implemented. The
reasons for choosing this protocol where as following:
The wave blocks are to be transmitted quite often (up to 300 times per second) and sometimes they
contain only one channel of information. For this single channel, one needs at least: a block header, a
counter, a checksum and the wave sample value itself. To reduce overhead, the number of wave samples
in package have been packed into one byte, together with the checksum. The checksum for the wave
packet is therefore only 4 bits long, because the remaining four bits are needed for the wave counter. The
status and the value blocks use 7 bit checksums. There is still enough security, because each byte has its
own parity bit.
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