Omron E5ZD, Руководство по эксплуатации

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53
3-2-2 Block Format
The character string transmitted by the host computer is called an command
block. The character string returned by the E5ZD is call a response block. Each
character in the string is sent as 8-bit ASCII (see Appendix D). In this manual,
characters are numerically referred to as the hexidecimal equivalent of the
ASCII code. One generalized block is shown below.
@ 0 X X X X X X X X X CR
Header code
*
Terminator
Address Data code Text FCS Always 0.
8 bits
Range for FCS calculation
Unit Bank Point
Start character
(2 letters)
Each block begins with a start character, @ (40
hex
), and the unit number of the
E5ZD which is to receive or send the block, and ends with an FCS and a termina-
tor. The data code identifies the type of text being transmitted. The unit number
must be between 0
hex
and F
hex
. The terminator consists of * (2A
hex
) and a car-
riage return (0D
hex
).
3-2-3 Communications Errors
All communication errors and recovery from them must be processed at the host
computer. A program must therefore be loaded into the host computer to detect
errors and execute the necessary steps to recover from them.
Transmissions should be set up to be repeated about ten times in order to deal
with communications errors resulting from noise. If noise-originating errors oc-
cur too frequently, either try a lower baud rate or use an optical interface.
E5ZD Checks Error checks at the E5ZD are performed both by character and by block.
Characters are checked via vertical parity, a framing check, and an overrun
check. Even parity is used with an exclusive OR performed by character. If the
stop bit is found to be a 0, it will result in error generation. Finally, if the next char-
acter is received before the current character has been processed, an error is
generated.
Block checks include checking the command format, numeric values, point
number designations, and FCS (see the next section).
FCS Calculations An FCS (frame check sequence) must be sent with every command block and is
returned with every response block. The FCS in each response block should be
checked at the host computer to confirm correct transmission.
The FCS is calculated as the exclusive OR of all characters from the start char-
acter through the final data character, as shown below. The resulting 8-bit value
Communications
Section 3-2