A telegram octet refers to the 8 bits representing the actual useful information.
A telegram serial character refers to the bits required in order to exchange telegrams physically via TP1 signals.
Each TP1 signal represents 1 bit, i.e. two TP1 signals have been defined:
- passive signal: representing a logical '1'
- active signal: representing a logical '0'
A TP1 serial character has a length of 11 bits:
- 8 bits representing the telegram octet
- 3 additional bits
The 3 additional bits for TP1 are:
- 1 start bit, sent before the LSB of the telegram octet
- 1 even parity bit, sent after the MSB of the telegram octet, which is also known as the vertical parity check
- 1 stop bit, sent after the even parity bit