How can I put the direct signal MCLR using the FT232? (ICD2)

[ea7fnj]

Hi guys.

I'm designing my own ICD and I have seen a lot of schematics. I have been seeing the signals about ICD:

- (RC5 > PGD_T out / RC4 > PGD_T in) RA5 > switch I/O PGD_T
- (RC3 > PGC_T I/O) RA2 > switch I/O PGC_T
- (RB7 > PGM_T out) RB1 & RB6 switch PGM_T out

- RA4 switch the VCC_T
- RC0 switch the VPP to MCLR_T
- RC1 switch the VCC to MCLR_T
- RC2 switch the GND to MCLR_T

- AN0 watch the MCLR_T voltages
- AN1 watch the VCC_T
- AN3 watch the VPP

- RB3 is the BUSY led
- RB1 is the ERROR led
- VCC with the POWER led

- T1IN > RC6 / R1OUT > RC7
- T2IN > RB5 / R2OUT > RB4

Those are the signals in ICD circuit, but I see the RS232's pin 4 is direct to PIC's MCLR pin and the PROG header. I would like to use the FT232 USB <> 232 TTL, but if this signal comes from COMx of PC, maybe it's about 12V.

The question is: How can I put the direct signal MCLR using the FT232? Can I use a PNP transistor to switch this signal with 12V? Any idea?

Thanks

 

[RedFloyd]

Re: ICD2 signals

Hi,

in fact, the pin 4 of the RS232 connector is not directly connected to the MCLR of the PIC. This pin is used to reset the pic, so you need 0V to 5V signal. If you look carefully on the drawings that are availlable, you'll see that there is a resistor and a zener diode connected to the pin 4 of RS232. These components are used to limit the voltage to 0V and to 5V.

So, when using the FT232 chip, you can connect the MCLR pin of the PIC to the pin 21 of the FT232 chip, but be aware that this signal is active low, so you need to use any kind of inverter (logic ic or transistor). This pin is the DTE ready output signal, so it's the same signal as on the pin 4 of the RS232, but in logic level instead of RS232 level voltages.

Hope it helps!