PIC16LF1455 ICSP programming using D+/D-

[email protected] · Joined: 18 Apr 2018 Posts: 5

Hi,

I am working on PIC16LF1455 microcontroller, with MPLAB X IDE v4.10 and CCS compiler (v5.062). The ICSP programming through RC0 and RC1 (pin 10 and 9) works fine. See the figure for the pinout.

Now I am trying to use RA0 and RA1 (pin 13 and 12, or D+ and D-). The datasheet says D+ / D- pins should be enabled for low voltage programming (LVP) mode. But I tried LVP model, I got following error message:

"The low voltage programming feature requires the LVP configuration bit to be enabled on the target device. Please enable this configuration bit and try the operation again."

But I have set the LVP on in the program, but no effect.

#pragma config LVP = ON

Any suggestions?

Perry

temtronic · Posted: Wed Apr 18, 2018 9:40 am

Well I downloaded the datasheet and it's not crystal clear to me..though maybe cause I'm getting old ?..... I'd have thought in the 'ISP' section, they'd explain in detail how to use both methods.
It appears to me there are 2 methods of ICSP. 'Normal' (using HV) done on 99.44% of PICs and then 'LVP' which is not commonly used.
One problem is that you'll need to tell the programmer to do 'LVP' . Depending on the programmer that can be done in a pulldown window or, with PK3, you can have the actual program do it.
I've never acually used LVP in 2+ decades....
but...
have do a question
Why use the D+D- pins? I assume you're using this PIC as it has USB. If so you need to isolate the ICSP pins from the USB hardware and that could be tricky. Even using 'regular' PICs, I keep ICSP pins only for ICSP function as I was 'bit' once trying to use the pins for both ICSP and I/O use.
Jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19496

You realise that you are going to have to program the LVP bit with the normal programmer _before_ you can use LVP to re-program the chip. The LVP bit cannot be set using LVP.

You also need to be very careful that the LVP lines are biased to ensure they do not come 'on' when the programmer is not attached.
Have a pull-up resistor on the ICSPCLK line.

[email protected] · Joined: 18 Apr 2018 Posts: 5

Thanks, Jay!

Using D+/D- pins can make the PCB simpler, no need to have an extra ICSP connector.

[email protected] · Joined: 18 Apr 2018 Posts: 5

Ttelmah · Joined: 11 Mar 2010 Posts: 19496

No. You leave LVP on.

You have to have the LVP enabled, program this with the high voltage programmer, and then leave it enabled.

LVP cannot write the LVP bit. It has to be written with a high voltage programmer before LVP will work.

temtronic · Posted: Thu Apr 19, 2018 5:07 am

re: Using D+/D- pins can make the PCB simpler, no need to have an extra ICSP connector.

hmm.. except as Mr. T points out you need to use HV ICSP at least once ! That means extra time, say 15 minutes per unit to attach to programmer, burn and confirm versus the cost of a 5 pin header. You also need the ICSP header, oopsy !!
Consider your time at $60 /hr (less than ANY tradersperson here). 15 minutes is $15, a 5 pin header is, at most, 15 cents. This might ba a case of 'penny wise- pound foolsh'.
I don't see this 'feature' being a good one from Microchip. It'd be nice to hear from a real user of it, perhaps the guy who 'thought it up', sounds good on paper but useful in the real World ? Mind you I still prefer 'big' PICs with lots of pins, memory and peripherals. Saving a days R&D $ ( 500-1000) can pay for a lot of the next 'bigger' PIC, especially when the client needs another LED !
Just food for thought.
Jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19496

LVP on the D+/D- pins, is for 'reverse compatibility' only. For code that was fundamentally written for the older pre-USB chip.
If you use these pins for LVP you basically lose the USB ability of the chip.
You also lose the MCLR pin. This becomes permanently enabled as MCLR only.
Now you need GND, MCLR, D+, D- Four connections. Not exactly a major saving over the standard ICSP header....

I quote from a poster on the MicroChip site about LVP on the same chip: