16F628A doesn't respond

[julianhaddad]

hi everyone. I have a problem trying to program PIC16F628A.
I have a home-made programmer like **broken link removed**. It works perfectly fine width 16F84A and I want to use it width 16F628.
The problem is that I can't read the 16F628A memory (program, data or configuration) I get all 0s.
I've checked the datasheets of both PICs a lot of times. They use same commands.
Tension levels are MCLR = 11.70v, VDD=5.05
Delay times are over 10ms between every command
RB4 (PGM) is pin connected to GND, and MCLR rises before VDD. I can't find any other difference.
Thanks everyone in advance, and pardon my english

 

[Nigel Goodwin]

As it doesn't switch Vdd it won't work with any PIC programmed to use it's internal oscillator - the 16F628a is one such device, you will only be able to program in once - after that, if it's set to use the internal oscillator, you can't reprogram it.

 

[julianhaddad]

I don't exactly know what do you mean width switching Vdd, but I have connected Vdd through a jumper and I make Vdd to rise (manually) after MCLR does. Can it be just noise in Vdd pin?

 

[Gayan Soyza]

I programmed with a similar programmer before I shifted to a USB programmer.It has Vpp,Vdd Timings.

 

[HATHA]

hi julianhaddad
Mr.Nigel said if mcu has a built in oscillator (like in 16f628A) and to program such a chip you have to supply vpp ( or voltage to mclr ) before vdd. otherwise chip will try to execute program which will already hade insted of program it
try to use winpic program soft, and i think your vpp should 13v isn't it?

 

[julianhaddad]

The range of tensions for Vpp is form 10 to 13.5v (according to Microchips datasheet).
I'm writing a c++ program using LPT1 port. Is there a maximum time between Vpp and Vdd?
Thanks all for the help.

 

[blueroomelectronics]

Simple parallel port programmers may not have the extra circuitry to switch on VPP before supplying the 5V VDD power. Post your programmer schematic.

 

[julianhaddad]

the programmer is like **broken link removed** with 2 modifications. pin10 (PGM) is connected to GND and pin1-pin14 are connected to Vdd through a jumper witch I enable manually. I'm going to try to use a BC548 and an extra output from LPT1

 

[julianhaddad]

OK so I switch Vdd via the LPT1. Still doesn't work but now I get some 1s.
Is it possible that my program is slow? is there a max limit on delay times?

 

[mvs sarma]

the programmer is like **broken link removed** with 2 modifications. pin10 (PGM) is connected to GND and pin1-pin14 are connected to Vdd through a jumper witch I enable manually. I'm going to try to use a BC548 and an extra output from LPT1

why not switch to the programmer indicated by Gayan Soyza? you could home brew one with so much details given.

 

[julianhaddad]

why not switch to the programmer indicated by Gayan Soyza? you could home brew one with so much details given.

Well... this is a didactic proyect so I prefer something easier to understand. (before using serial port)
Thanks anyway for the suggestions.

 

[mvs sarma]

Well... this is a didactic proyect so I prefer something easier to understand. (before using serial port)
Thanks anyway for the suggestions.

Many a times we are to use some equipments , even made by us at home. We may not understand them. if you make it exactly as described, it would perform. Understanding and analysis could be later. you can start using a PIC programmer and advance further in learning program writing and testing.

. For example , in elementary an education we are taught the formula for volume of a sphere V=4/3( ΠR³) where Π is (pie)