Migration from 16F877 to 18F452 problems

[Ronald]

Hi,

i've been having problems getting a simple LED to light on my 18F452. Works perfectly well for my 16F877 but not 18F452.

both are 40 pin DIL/PDIP, and i've been working with the 16f877 till today, when i discovered it was lacking in RAM. So i took out my 18F452 and stuck it in its place on my breadboard. prior to that i check that the pins were the same, except for the LVP pin which i didnt care abt. (If i'm wrong to just replace it pin for pin, can someone pls let me know)

env is MPLAB, ICD2, with CCS PCWH compiler.

code is basic:

#include <18F452.h>
#device ICD = true

#fuses XT, NOWDT, NOLVP, NOPROTECT


main()
{
output_high (PIN_A2);
}

works perfectly well for the 16f877 (just by changing the header file), but not 18f452.
osc is a 4 legged 20Mhz.
compiles correctly, programs very well, but the LED just doesnt light up. I've tried it with other pins too, but they dont work as well.

Greatly appreciate any help. If someone could tell me what to put in the config bits part i'll be most happy.

thanks,
ronald

[daveroll]

check the osc waveform for correct applitude

change xt to hs.

add the fuse nodebug

program the device with programmer not debuger

unplug the icd2 after programing it

power down the 452 and power it up

[lesotter]

Not sure if this is yur problem, but when I ported an app from 16f877 to 18f452 I needed to add

#byte PORTA = 0xf80 // for 18f452

before any activity could be used on the A port.

Also, try disabling the a/d by :-

SETUP_ADC_PORTS(NO_ANALOGS);

and

set_tris_a(0); //to make A port outputs

[ckielstra]

[Ttelmah]

The reason it 'works', is because he is using an external oscillator (4pin crystal in the original post), so the gain of the internal oscillator, doesn't really matter (which is what XT/HS changes). I agree EC would be a better 'choice'.
The code is incorrect for both chips, because the ADC, is not disabled. The reason for the difference though, is that the I/O behaviour is fractionally different, on the two chips, with the 877, overriding the peripheral, if the pin is selected as an output, while the 452, _requires_ you to disable the periperal. Adding 'setup_adc_ports(NO_ANALOGS);', should make the code work.

Best Wishes