7

ATA6830

4575C–BCD–05/03

Figure 6. Synchronization Sequence

Between two commands a pause has to be included. This is necessary for a clear rec-

ogition of a new message frame (command). Figure 7 shows the timing diagram of two

commands.

Figure 7. Message Frame and Space

Every command consists of 16 bits. They will be sent with two bytes. Figure 8 shows the

message 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 recognized due to a transmission error (parity error), the

entire command is rejected.

Figure 8. 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