7

4575D–BCD–09/05

ATA6830

Figure 3-4.

Synchronization Sequence

Between two commands a pause has to be included. This is necessary for a clear recognition of

a new message frame (command). Figure 3-5 shows the timing diagram of two commands.

Figure 3-5.

Message Frame and Space

Every command consists of 16 bits. They will be sent with two bytes. Figure 3-6 shows the mes-

sage frame. The high byte is sent first, immediately followed by the low byte. Every byte starts

with a start bit and ends with a parity bit and a stop bit. The first start bit (level 0) after a pause

(level 1) indicates the beginning of a new message frame. The value of the parity bit has to be

odd, i.e., the crossfooting of the byte including the parity bit is odd. If a data packet is not recog-

nized due to a transmission error (parity error), the entire command is rejected.

Figure 3-6.

Command Bits

START

BIT

STOP

BIT

PARITY

BIT

PARITY

BIT

STOP

BIT

START

BIT

SYNCHRONIZATION PATTERN

MESSAGE FRAME

HIGH BYTE

LOW BYTE

SPACE

7

HIGH BYTE

START

BIT

STOP

BIT

6

5

4

3

2

1

0

PARITY

BIT

8 DATA

BITS

7

6

5

4

3

2

1

0

PARITY

BIT

8 DATA

BITS

LOW BYTE

STOP

BIT

START

BIT

MESSAGE FRAME