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A variety of communications cables and settings were discussed.
* ASCII functions are available of PLCs making serial communications possible.

27.6 PRACTICE PROBLEMS

1. Describe what the bits would be when an A (ASCII 65) is transmitted in an RS-232 interface with 8 data bits, even parity and 1 stop bit.
1. Divide the string in ST10:0 by the string in ST10:1 and store the results in ST10:2. Check for a divide by zero error.
2. ST10:0 “100” ST10:1 “10” ST10:2
2. How long would it take to transmit an ASCII file over a serial line with 8 data bits, no parity, 1 stop bit? What if the data were 7 bits long?
3. Write a number guessing program that will allow a user to enter a number on a terminal that transmits it to a PLC where it is compared to a value in N7:0. If the guess is above "Hi" will be returned. If below "Lo" will be returned. When it matches "ON" will be returned.

plc serial -27.16

5. Write a program that will convert a numerical value stored in F8:0 and write it out the RS-232 output on a PLC-5 processor.

27.7 PRACTICE PROBLEM SOLUTIONS

before start data parity stop

1.
2. If we assume 9600 baud, for (1start+8data+0parity+1stop)=10 bits/byte we get 960 bytes per second. If there are only 7 data bits per byte this becomes 9600/9 = 1067 bytes per second.

plc serial -27.17

4.
R6:4/EN ACB
Channel 0
Control R6:4
EQU SourceA R6:4.POS Source B 2 ARL Channel 0 Dest ST9:0 Control R6:0
Length 3
R6:0/DN ACI
Source ST9:0
Dest N7:1
LES AWT
Source A N7:1 Channel 0
Source B N7:0 Source ST9:1
Control R6:1
Length 2
EQ AWT
ST9:1="Lo" ST9:2="ON" ST9:3="Hi" Source A N7:1 Source B N7:0 Channel 0 Source ST9:2 Control R6:2 Length 2
GRT AWT
Source A N7:1 Channel 0
Source B N7:0 Source ST9:3
Control R6:3
Length 2