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PDT 1100 Product Reference Guide
bit positions of the character to be transmitted, respectively. A clock starts counting when it
receives the start bit and it stops communicating when the stop bit is received. The number
of the stop bits is selectable (1 or 2 bits).
Optical Interface Communications Range
The optical interface's maximum effective range is 30 inches (80 cm) with the IR beam
within a 10° angle of divergence.
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 PDT 1100 is 7- or 8-bit code. The transmission bit order is LSB (Least
Significant Bit) first. Following is an example for transmitting character A (41h, 01000001b)
coded to 8-level code with an even parity and a single bit for start and stop bits.
LSB
1
0
0
0
0
0
1
0
0
Start Bit
Stop Bit
Parity Bit
Figure A-2. Transmission Example
Response Method
When two devices initiate communications, they exchange signals for correct data
transmission. This procedure is called "handshaking" or "data link establishment phase."
The sender sends a control code ENQ (05h) to inquire if the receiver is ready to receive
data, and the receiver replies with a control code ACK (06h)(positive) or NAK
(15h)(negative) to start data transmission.
Vertical Parity
A vertical parity bit is a redundancy bit added to every character to be transmitted 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 immediately follows the MSB (Most Significant Bit) as shown in
Figure
A-3.
A-6
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