User`s manual

BD2-1220/1221 User’s Manual

7.4 Data Structure

(1) Start bit

Status is read again 1/2 bit after a negative transition from Mark to Space. If the status is at Space, it is

recognized as a Start bit.

If the status is at Mark, it is not recognized as a Start bit. Start bit detection is attempted again without

causing an error.

(2) Data bits + parity bit

Data and parity bits are sampled over 1-bit time period following the 1/2 Start bit. The bit configuration is:

Start bit, bit 0, bit 1, ....., parity bit.

(3) Stop bit

A stop bit is a Mark state of 1-bit length or more. A framing error occurs if a Space is detected at a stop bit

sense timing.

7.5 Error Detection

Detection of parity errors, framing errors, and overrun errors is provided with this control board. When an

error is detected, the data containing the error is stored in the buffer as a “?”.

(1) Framing error

If a space state is detected at the timing of stop bit detection, this indicates that an error has occurred. The

data containing the error is stored in the buffer as a “?”.

(2) Parity error

With parity check specified, when data is parity-checked and an error is detected, the data containing the

error is stored in the buffer as a “?”.

(3) Overrun error

If an overrun error is detected, the data containing the error is stored in the buffer as a “?”.

(3)(2)(1)

(1)

(2)

(3)

Start bit

Data bits (+ parity bit)

Stop bit

h0, h1, h2

Mark

Space