Should I need to connect Vcap for programming a PIC16F727?

[radioshack]

I am having trouble talking to this PIC with a PicKit2 via MPlab.

I have prog'd more basic 18 pin 16f's with the pickit2, but cannot communicate with this device.

I read that these ICs run on a low-voltage core and require a LDO dropdown cct and this needs a separate cap to stabilise the 3.3v internal ref for the core.

Am I getting this right?
Thanks.

 

[mvs sarma]

use 'under device family' "mid Range/1.8V min Configuration" then you can select the 16F727. for details read "read me" under help of Pickit2 driver v2.61 and similar arrangement under pickit2 would be there.

 

[Gobbledok]

Yes you need a 0.1 - 1uf ceramic cap on one of the available vcap pins. If you don't have one it can surely cause you issues communicating with the chip with your PicKit. I believe you also have to set the config word properly for the pin which has the vcap.

Read the datasheet, section 5, Low Drop out Voltage Regulator.

 

[radioshack]

Thanks for the replies.

I'm confused about how I would go about setting the config word if I can't even establish comms with the device though - ?

I will fit a cap in the meantime.

 

[mvs sarma]

most probably you might have interchanged the data and clock wires. please check

 

[Gobbledok]

Thanks for the replies.

I'm confused about how I would go about setting the config word if I can't even establish comms with the device though - ?

I will fit a cap in the meantime.

Yeh it's a bit of a funny setup with the Vcap pin selection but give it a try and see how it goes. Perhaps all of the pins are connected to the internal voltage regulator until the config word is set? Can't hurt to try.

 

[radioshack]

Thanks mvs - will check data &clk lines (again) - not able to right now unfortunately.

I had wondered if I had initially wired Vdd & Vss back to front on the breadboard and had have killed the chip.

In my (limited) experience PICs seem fairly hardy and I've checked if current is being drawn on Vdd - and about 4.5mA is, if memory serves.

 

[mvs sarma]

it might not die so easily,LoL, try to use Vpp first option if you are using int osc and mclr off

 

[Gobbledok]

Haha yeh they are hardy little things. I've had an '877 almost too hot to touch on my breadboard and it still worked