Pickit2 to Development board.

[richard.c]

Hi all,

I've got a MicroChip Pickit2 programmer that I connect to my own little dev board.

Unfortunately my projects all use Rb6 and Rb7 programming lines and sometimes Mclr / Re3.

I currently use a 4 pole switch to isolate these lines while the programmer does it job.

I know electronic switches like the 4053 etc are capable of handling these lines, but what I would like to know, is there any way the Pickit2 can enable these chips when it wants to program, so alleviating the need for constant manual switching ?



Thanks

Richard

 

[nickelflippr]

The PICkit 2 user guide shows how to isolate the icsp/clk, icsp/dat, and MCLR lines. Also has rules for debugging.

 

[richard.c]

Yes, thanks, - have seen all that info, but unfortunately it doesn't actually let me know if any signal from the Pickit2 will be able to control the switches while programming is done.

 

[nickelflippr]

Right, was thinking of a passive solution.

Just brainstorming here.

Maybe a combination of the two would be the answer. The sticking point that I see is the MCLR/VPP pin as it will always be a '1'. If you can spare the voltage drop, put the diode on the MCLR line like the data sheet. Run a leg off the MCLR/VPP connection, consisting of a load limiting resistor and say a 10V zener. Tie the leg to A, B on the 4053, so when the PICkit 2 is programming, the normal on channels ax, bx (Rb6 and Rb7) go to ay, by (icsp/dat and icsp/clk)?

 

[blueroomelectronics]

Another problem might be since you're using MCLR (RE3) as I/O you won't be able to get the PIC into programming mode unless you let the PK2 control VDD also. (VPP before VDD)
The VPP +13 controlling the 4053 might work, not sure if a 4053 can handle voltage (VPP) higher when powered by 5V through its analog switches?

CD4051BMS, CD4052BMS and CD4053BMS analog multiplexers/ demultiplexers are digitally controlled analog switches having low ON impedance and very low OFF leakage current. Control of analog signals up to 20V peak-topeak can be achieved by digital signal amplitudes of 4.5V to 20V (if VDD-VSS = 3V, a VDD-VEE of up to 13V can be controlled; for VDD-VEE level differences above 13V, a VDDVSS of at least 4.5V is required). For example, if VDD = +4.5V, VSS = 0, and VEE = -13.5V, analog signals from - 13.5V to +4.5V can be controlled by digital inputs of 0 to 5V. These multiplexer circuits dissipate extremely low quiescent power over the full VDD-VSS and VDD-VEE supply voltage ranges, independent of the logic state of the control signals. When a logic “1” is present at the inhibit input terminal all channels are off.

 

[nickelflippr]

Scratch that idea, my eyes were crossed when looking at the CD4053 data sheet. The further you look into the digital switch idea, the deeper in trouble you get, or so it seems. Don't the passives work like the data sheet proposes?

 

[nickelflippr]

Will swing the bat one more time. Could use previous idea of using VPP with a load limiting resistor and 10V zener for control leg of the 4053. Only, add yet another 5.0V zener off that leg so your input corresponds to the 5V Vdd of the chip. With that scenario you could use a faster 74HC4053 to control the icspdat and icspclk lines. Still no garuantees.

 

[blueroomelectronics]

There are PIC with scads of I/O and some even have two ICP ports.
Also it's often possible to put more than one device on a single port, LCDs are often muxed with other things on the same port. Without seeing your schematic its impossable to tell.
Which PIC are you using?