Set64RS-Temperature-Controller

Set64RS notes

Main Board

• CPU chip = Media:16F76-I/SO
  • RC6 / TX / CK > pin 17 - TX Goes to 485 circuit
  • RC7 / RX / DT > pin 18 - RX goes to 485 circuit
  • RA4 / T0CKI > pin 6 - TXEN goes to 485 circuit ( T0CKI = Timer 0 Clock input )

PIC chip > 193 bytes RAM / 4096 words of program memory

CD4051B - 8 channel mux / demux

74hc164

24LC64 > 64 kbit serial eeprom 9 ( 8 kbytes )

crystal frequency = 18.432 MHz > 1920X 9600 baud

Comments

• Why does the TXEN line go to the rs-485 circuit? direction control?

• • Naming convention **TXEN** is suspicious = Transmit Enable ?? > most likely
  • Most likely the 18.432 xtal is the timing oscillator for serial bus. 18.432 / 1920 = 9600 baud
  • Most likely the TXEN controls flow and RA4 is used as in input output pin for this and not to connect to timer0

Notes from user manual

• Comm port settings
  • speed > variable and can be set from menu
  • Stop bit = 1
  • Data Bit = 8
  • parity = none

• ModBus > From manual...function codes
  • 03 > read
  • 01 > read the status
  • 05 > change control pattern > auto tuning etc

...did not have WRITE code

• Addresse ranges called out in manual
  • 1000,2000,3000,4000 hex

Conclusions

• Most likely could setup a circuit using TXEN as flow control with TX and RX going to line receiver / transmitter.

• • would need to figure out TXEN states > HIGH is TX or RX enable?? Should be listening when in quiescent state. Thus measure it when just sitting there.

• • fitting a transceiver > would not know polarity of the signal going to the processor. A / B signals should put out HIGH / LOW when? A = high or B= high ???

• The comm protocol is more difficult as I have no example. I have addresses of registers but no examples.

• Difficult when the hardware AND software are in doubt.