16f84 / 16f88 port a differences

Started by Lez August 9, 2005

Built the 2 resistor serial link as shown in some pic basic PDF files,
and I have had no problem with the 16f84 (1k for pic serout, 22k for serin)

re-compiled the program for a 16f88, plugged chip in, data from chip to
PC is ok but data from PC to chip is not being seen by the PIC.

I have led's on the lines, both led's glow when data is moving, and
typing on the PC keyboard flashed the LED, but the pic does nothing.

Resistor change? more / less value ?
Tried a wet finger it changes the led brightnes so I must be missing
something else about this port.

Also tried a 648a and a 628a, both do same as f88.

I am receiving data on a.0, sending data back to the pc on a.1

I use a.2 as a 'ready to receive' led and that is fine.
I use a.3 as a 'ready and powered' led and that is not coming on at
all(except on the f84)

led's have a 1k resistor to gnd I thought the f88 and f84 were 'compatible' ?

Quit and buy more 16f84's ?



--- In piclist@picl..., Lez <lez.briddon@n...> wrote:
>
> Built the 2 resistor serial link as shown in some pic basic PDF files,
> and I have had no problem with the 16f84 (1k for pic serout, 22k for
serin)
>
> re-compiled the program for a 16f88, plugged chip in, data from chip to
> PC is ok but data from PC to chip is not being seen by the PIC.
>
> I have led's on the lines, both led's glow when data is moving, and
> typing on the PC keyboard flashed the LED, but the pic does nothing.
>
> Resistor change? more / less value ?
> Tried a wet finger it changes the led brightnes so I must be missing
> something else about this port.
>
> Also tried a 648a and a 628a, both do same as f88.
>
> I am receiving data on a.0, sending data back to the pc on a.1
>
> I use a.2 as a 'ready to receive' led and that is fine.
> I use a.3 as a 'ready and powered' led and that is not coming on at
> all(except on the f84)
>
> led's have a 1k resistor to gnd > I thought the f88 and f84 were 'compatible' ?
>
> Quit and buy more 16f84's ?

The porta pins that you are using are also used by the A/D converter.
You need to ensure that they are configured as digital I/O and not
analog inputs. Check the data sheets.

Regards
Sergio Masci

http://www.xcprod.com/titan/XCSB - optimising PIC compiler
FREE for personal non-commercial use
.



Hi Lez,

Had that happen to me on the '877. ADCON0 = 0; /* A/D off */
ADCON1 = 6; /* all digital inputs */

HELPS! The A/D defaults ON. Another pair that got me:

CVRCON = 0; /* turn off compare modules */
CMCON = 7; /* 7 is power on reset, */

Although these are defaults, and can probably be ignored. I inadvertently
set CMCON = 0, thinking to turn 'em off, but that was wrong!

'88 has these registers, but I don't know off hand if these are the same in
an '877.

Alan KM6VV
> -----Original Message-----
> From: piclist@picl... [mailto:piclist@picl...] On Behalf
> Of Lez
> Sent: Tuesday, August 09, 2005 12:53 PM
> To: piclist@picl...
> Subject: [piclist] 16f84 / 16f88 port a differences > Built the 2 resistor serial link as shown in some pic basic PDF files,
> and I have had no problem with the 16f84 (1k for pic serout, 22k for
> serin)
>
> re-compiled the program for a 16f88, plugged chip in, data from chip to
> PC is ok but data from PC to chip is not being seen by the PIC.
>
> I have led's on the lines, both led's glow when data is moving, and
> typing on the PC keyboard flashed the LED, but the pic does nothing.
>
> Resistor change? more / less value ?
> Tried a wet finger it changes the led brightnes so I must be missing
> something else about this port.
>
> Also tried a 648a and a 628a, both do same as f88.
>
> I am receiving data on a.0, sending data back to the pc on a.1
>
> I use a.2 as a 'ready to receive' led and that is fine.
> I use a.3 as a 'ready and powered' led and that is not coming on at
> all(except on the f84)
>
> led's have a 1k resistor to gnd > I thought the f88 and f84 were 'compatible' ?
>
> Quit and buy more 16f84's ?


To make the 16F88 behave like the 16F84 you just have to disable the
analog functions.

In Assembly:
banksel cmcon
movlw 7
movwf cmcon
clrf ansel
banksel porta

In some high-level language:
CMCON = 7
ANSEL = 0 Mike --- In piclist@picl..., Lez <lez.briddon@n...> wrote:
>
> Built the 2 resistor serial link as shown in some pic basic PDF
files,
> and I have had no problem with the 16f84 (1k for pic serout, 22k
for serin)
>
> re-compiled the program for a 16f88, plugged chip in, data from
chip to
> PC is ok but data from PC to chip is not being seen by the PIC.
>
> I have led's on the lines, both led's glow when data is moving, and
> typing on the PC keyboard flashed the LED, but the pic does nothing.
>
> Resistor change? more / less value ?
> Tried a wet finger it changes the led brightnes so I must be
missing
> something else about this port.
>
> Also tried a 648a and a 628a, both do same as f88.
>
> I am receiving data on a.0, sending data back to the pc on a.1
>
> I use a.2 as a 'ready to receive' led and that is fine.
> I use a.3 as a 'ready and powered' led and that is not coming on at
> all(except on the f84)
>
> led's have a 1k resistor to gnd > I thought the f88 and f84 were 'compatible' ?
>
> Quit and buy more 16f84's ?