Cannot read 12F675 with ICSP

Hi all!

I've searched the forums here and haven't come up with a solution that works for me. I can program my PIC, but cannot read from it. I have a PIC 12F675 hooked up to a JDM programmer and am using WIN PIC for programming it.

The Vpp is being raised to 12.75 volts. What value should this be? The datasheet for the 12F675 doesn't specify the exact value, oddly enough, just referencing a programming reference manual, which I cannot find.

Everything works just fine (read/write) when using the DIY K-149 programmer. However, when I use the ICSP off of the K-149 to the same DIP 12F675, it too cannot read. This is using the MicroPro DIY K149-BC PICMicro Programmer v141204 and protocol P018.

I even hooked up the PIC straight onto the ICSP programming wires. How is it possible that I can write but not read??

Any suggestions?

Thanks,
Dan

are you pulling mclr up internally and using the internal osc? I believe JDM programmers have a problem with that. some where I saw a fix for that.

JDM programmers tend to be unreliable anyway, but ICSP requires a programmer specifically designed for that, which the JDM isn't. How long are your leads from programmer to PIC?, they need to be REALLY short.

Some of the programmers that are available apply VDD all the time. The 675 requires VPP to be applied before VDD in order to enter programming mode. Problems manifest themselves when you use the internal clock and disable MCLR. In this state, applying power will cause the programmed code to run and prevent programming mode being entered. A simple solution to this problem is to disconnect VDD and connect a 1k resistor from VPP (MCLR) to VDD and a 5.1V zener from VDD (cathode) to ground, thus ensuring VPP is applied first. Be aware that this mod may stop you programming some other pics like the 16F88.

Mike.
Nigel, A Friend of mine recently had problems with your tutorial. The problem turned out to be as described above. He programmed tutorial 1.2 and although WinPic said it had failed to program it, the data in line was pulsing and the code was running while the chip was still in the programmer. This also happened with IC-PROG. The programmer was the one published by Silicon Chip magazine. The above mod fixed it.

You can find the programming specification Here.

Mike.