Is it possible to use ICSP with PIC18LF452 at Vdd=3.3v?

[Tyler Coen]

I've been trying to program a PIC18LF452 using ICSP with Vdd=3.3V. The setup works fine when Vdd=5V. I am not using low-voltage programming (meaning the MCLR/Vpp pin is brought to 13V when programming).

The datasheet indicates that Block Erase cycles require a Vdd of at least 4.5V. All other ICSP cycles are supported at all operating voltages.

I think that the programming software i've tried (MPLAB and EPIC) use these block erase cycles to erase the chip before
programming and thus won't work when Vdd=3.3V.

Does anyone know if this is the case? If so, is there programming software that doesn't use these block erase cycles.

Is it worth taking the time to write my own programming software that doesn't use these cycles? Or is there a more fundamental problem? If so, it seems kinda silly for Microchip to make a low-voltage (less than 5V) part that can't be programmed at low-voltage (at least not in-circuit).

My project is a bit stalled at this point. Any help would be greatly appreciated.
Thanks
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This message was ported from CCS's old forum
Original Post ID: 144516438

[John Yaron]

:=I've been trying to program a PIC18LF452 using ICSP with Vdd=3.3V. The setup works fine when Vdd=5V. I am not using low-voltage programming (meaning the MCLR/Vpp pin is brought to 13V when programming).
:=
:=The datasheet indicates that Block Erase cycles require a Vdd of at least 4.5V. All other ICSP cycles are supported at all operating voltages.
:=
:= I think that the programming software i've tried (MPLAB and EPIC) use these block erase cycles to erase the chip before
:=programming and thus won't work when Vdd=3.3V.
:=
:=Does anyone know if this is the case? If so, is there programming software that doesn't use these block erase cycles.
:=
:=Is it worth taking the time to write my own programming software that doesn't use these cycles? Or is there a more fundamental problem? If so, it seems kinda silly for Microchip to make a low-voltage (less than 5V) part that can't be programmed at low-voltage (at least not in-circuit).
:=
:=My project is a bit stalled at this point. Any help would be greatly appreciated.
:=Thanks

Tyler,

Did you figure out anything else on this ? I designed
a flashing unit and was wondering if my 3.3V uC's will
have trouble flashing.

thanks
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This message was ported from CCS's old forum
Original Post ID: 144516527

[Tyler Coen]

:=Tyler,
:=
:=Did you figure out anything else on this ? I designed
:=a flashing unit and was wondering if my 3.3V uC's will
:=have trouble flashing.
:=
:=thanks

Yes, I was able to eventually program the PIC18LF452 in circuit with Vdd=3.3V. There is a catch though when using the 18LF series.

Like the datasheet says, the block erase cycles are not available at 3.3V. This means that if you enable any code protection then you will not be able to undo this and subsequent attempts to program will fail (unless you use a Vdd of 5V). Just disable ALL of the code protection options and it should work fine. Also check that CCS is generating the fuses correctly (I had an old version, 3.120ish, and the fuses were incorrect, 3.148 seems ok though).
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This message was ported from CCS's old forum
Original Post ID: 144516530

[John Yaron]

:=:=Tyler,
:=:=
:=:=Did you figure out anything else on this ? I designed
:=:=a flashing unit and was wondering if my 3.3V uC's will
:=:=have trouble flashing.
:=:=
:=:=thanks
:=
:=Yes, I was able to eventually program the PIC18LF452 in circuit with Vdd=3.3V. There is a catch though when using the 18LF series.
:=
:=Like the datasheet says, the block erase cycles are not available at 3.3V. This means that if you enable any code protection then you will not be able to undo this and subsequent attempts to program will fail (unless you use a Vdd of 5V). Just disable ALL of the code protection options and it should work fine. Also check that CCS is generating the fuses correctly (I had an old version, 3.120ish, and the fuses were incorrect, 3.148 seems ok though).

So if I enable ext code protection (CPn bits) during
a VDD=3.3V flash, can I then subsequently go in again
and perform a full "chip erase" at VDD=3.3V and VPP=13V
to get the CP bits back to a '1'?
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516534

[Tyler Coen]

:=So if I enable ext code protection (CPn bits) during
:=a VDD=3.3V flash, can I then subsequently go in again
:=and perform a full "chip erase" at VDD=3.3V and VPP=13V
:=to get the CP bits back to a '1'?

No you cannnot perform a full chip erase at 3.3V. I'm not too clear on the exact details, and I don't want to experiment since I have to desolder a chip everytime I get stuck. I'm disabling all write/read protections and it works. Perhaps Microchip tech support would know if you can enable any of the code protection and still be able to reprogram at 3.3V.
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516563

[John Yaron]

:=:=So if I enable ext code protection (CPn bits) during
:=:=a VDD=3.3V flash, can I then subsequently go in again
:=:=and perform a full "chip erase" at VDD=3.3V and VPP=13V
:=:=to get the CP bits back to a '1'?
:=
:=No you cannnot perform a full chip erase at 3.3V. I'm not too clear on the exact details, and I don't want to experiment since I have to desolder a chip everytime I get stuck. I'm disabling all write/read protections and it works. Perhaps Microchip tech support would know if you can enable any of the code protection and still be able to reprogram at 3.3V.

uChip confirmed your findings. I have 3 uControllers on my
latest gadget...2-5V and 1-3.3V. I'm using a 33 ohm resistor on
VDD to 3.3V uC and also bringing out to pin 2 of 6 pin ICSP
header. Flasher unit will switch 5V to pin 2 to flash the
3.3V uC.... pain in butt, but, uChip tech supp claims there's
no immed plans to make uC's with '3.3V across all functions'
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516582