Denso BHT-6000 - page 100

Chapter 3. Communications Operations of BHT-6000

■ Transmission Code and Bit Order

All characters should be coded to 7- or 8-bit code for data transmission. The

standard data exchange code of the BHT-6000 is JIS 7- or 8-bit code. The transmis-

sion bit order is LSB (Least significant bit) first.

What follows is an example for transmitting character A (41h, 01000001b) coded to

JIS 8-level code with an even parity and a single bit each for start and stop bits.

Parity bit

Stop bit

Start bit

■ Response Method

When two devices initiate communications, they exchange signals for correct data

transmission. This procedure is called "handshaking." The sender sends a control

code ENQ (05h) to the receiver meaning "Are you ready to receive data?," and the

receiver replies to it with a control code ACK (06h) or NAK (15h) meaning "Positive"

or "Negative" for starting data transmission, respectively. This sequence is also

called "data link establishment phase."

■ Vertical Parity

A vertical parity bit is a redundancy bit which is added to every character to be

transmitted in order to check that data has been transmitted accurately. The parity

bit should be set to "1" or "0" depending upon the parity parameter setting, to make

the number of set bits in the character even or odd. The receiver counts the

number of set bits in the transmitted character code to make sure that it has the

selected number (even or odd) of set bits.

The vertical parity bit is positioned immediately following the MSB (Most signifi-

cant bit) as shown below.

(For 7-bit data)

Vertical parity bit

(For 8-bit data)

100000100

LSB MSB

b0 b1 b2 b3 b4 b5 b6

LSB MSB

b0 b1 b2 b3 b4 b5 b6

LSB MSB