Added PVs for PCF8591 ADDA chip interface

epics/iocs/ISTTOKrpi/protocols/pcf8591.proto

@@ -0,0 +1,44 @@
+Terminator   = "";
+LockTimeout  = 500;
+ReplyTimeout = 100;
+ReadTimeout  = 100;
+WriteTimeout = 100;
+MaxInput     = 1;
+ExtraInput   = Error;
+
+rReg {
+  out ${1};
+  in  "%.1r";
+}
+# To read adc write control Byte
+# Bits 0,1 ADC channel Selection
+# Bits 2 : ADC auto increment =0
+# Bits 3 : =0
+# Bits 4,5 ADC configuration . 00 = four single ended channels
+# Bits 6 : DAC Output enable bit
+# Bits 7 : =0
+
+rConvAdc0 {
+  out ${1} 0x00;
+  in  "%01r";
+}
+rConvAdc1 {
+  out ${1} 0x01;
+  in  "%01r";
+}
+rConvAdc2 {
+  out ${1} 0x02;
+  in  "%01r";
+}
+rConvAdc3 {
+  out ${1} 0x03;
+  in  "%01r";
+}
+
+##  @init { rReg; }
+##
+wReg {
+  out ${1} "%.1r";
+}
+
+