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johnl
Joined: 30 Sep 2003
Posts: 120
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| 16F1827 Weak Pullups work on Port B but not on port A |
 Posted: Fri Feb 26, 2016 2:02 pm |
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The assembly listing shows 0b11111 getting written to the WPUA register, but the datasheet says all but one bit of the WPUA register are unimplemented. So how do the individual port A pullups get configured? This code fails to enable the resistors on port A.
| Code: |
#include<16F1827.h>
#include<string.h>
#USE fast_io(B)
#USE DELAY (CLOCK = 32M)
#use rs232(baud=9600,xmit=PIN_b2,PARITY=N,BITS=8,STOP=1, errors)
#FUSES HS, PLL // High speed osc with HW enabled 4X PLL
#FUSES PUT // Power Up Timer
#FUSES NOBROWNOUT // No brownout reset
#FUSES NOWDT // No Watch Dog Timer
#FUSES MCLR // Master Clear pin used for I/O
#FUSES NOLVP // No low voltage prgming
#FUSES NOPROTECT // Code not protected from reading
#FUSES NOCPD // No EE protection
#byte PORTA = 0x0E
#byte PORTB = 0x0D
#define IN PIN_B4
#define ZEROtimer set_timer1(0)
#define LED PIN_B3
#define PULSE_OFF output_low( PIN_B3)
#define PULSE_ON output_high( PIN_B3)
long time;
int get_dmx(long );
long read_address(void);
int i;
int databit[8] = {0,0,0,0,0,0,0,0};
//=======================================
void main()
{
set_tris_b(0b11010011);
set_tris_a(0b00011111);
setup_adc_ports(NO_ANALOGS);
setup_timer_1 ( T1_INTERNAL );
port_a_pullups(0b00011111);
port_b_pullups(0b11010011);
while(1);;;;
} |
Assembly listing for the pullup functions:
| Code: |
6: port_a_pullups(0b00011111);
028 301F MOVLW 0x1f
029 0024 MOVLB 0x4
02A 008C MOVWF 0xc
02B 0021 MOVLB 0x1
02C 1395 BCF 0x15, 0x7
37: port_b_pullups(0b11010011);
02D 30D3 MOVLW 0xd3
02E 0024 MOVLB 0x4
02F 008D MOVWF 0xd
38:
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Feb 26, 2016 2:23 pm |
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The listing looks better in Symbolic mode:
| Code: | .................... port_a_pullups(0b00011111);
0026: MOVLW 1F
0027: MOVLB 04
0028: MOVWF WPUA
0029: MOVLB 01
002A: BCF OPTION_REG.WPUEN
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The 16F1827 data sheet says this:
| Quote: | 12.2.1 WEAK PULL-UPS
Each of the PORTA pins has an individually configurable
internal weak pull-up. Control bit WPUA<5> enables or
disables the pull-up (see Register 12-6).
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The 2nd sentence contradicts the first. Also, the WPUA register diagram
contradicts the first sentence. It says:
| Quote: | | bit 5 WPUA5: Weak Pull-up RA5 Control bit |
It appears that only pin RA5 has a weak pullup available on it. |
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johnl
Joined: 30 Sep 2003
Posts: 120
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| Posted: Fri Feb 26, 2016 2:37 pm |
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That's what I was afraid of. I am surprised there is no mention in the datasheet errata. Glad I didn't lay out the PCB yet.
Thanks for confirming. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19266
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| Posted: Fri Feb 26, 2016 4:02 pm |
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It's only confusing, since they bothered to have the 'general' weak pull-up register for PortA, which is normally reserved for chips that have individual weak pull-ups, but then only implemented it on the MCLR pin, and because of the extra paragraph that PCM_Programmer is pointing to.
Obviously CCS based their code on other chips that normally have the individual bits if there is a WPUA register. :(
However it is interesting how this has changed in the data sheet.
The original sheet doesn't have the section referring to individual pull-ups. It just has the diagram and all references are to RA5 only. The paragraph PCM_Programmer points to, was added in the 2011 data sheet (potentially contradicting itself), and is directly copied from a couple of other chips that do have weak pull up's on the other pins (1829 for example).
So the only erratum, is in the sheet. Should be pointed out to MicroChip, and CCS, should have it pointed out that only RA5 has this. |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Fri Feb 26, 2016 4:37 pm |
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The weak pull ups you want for the PIC in question come in convenient 1206/805/603 and even leaded packages and don't require programming to be on-duty even with power off...  |
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hmmpic
Joined: 09 Mar 2010
Posts: 314
Location: Denmark
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| Posted: Sun Feb 28, 2016 1:56 am |
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| If you can use a 14 pin chip then, 16F1825 have the WPU. |
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temtronic
Joined: 01 Jul 2010
Posts: 9136
Location: Greensville,Ontario
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| Posted: Sun Feb 28, 2016 6:30 am |
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I'll 'second' asmboy and point out that using REAL resistors remind you those I/O pins ARE inputs and better be high without an input to them !
Jay |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Sun Feb 28, 2016 10:12 am |
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BTW: smart designers use pull-ups & downs on OUTPUTS too- especially where a design critical initial state MUST be HI or LOW for safety/performance reasons.
During power down and reset - those output lines can float long enough to make real trouble in your design - while your pic code is getting its I/O together. Its the prime reason i faithfully #use fastio() and ALWAYS init my I/O TRIS in a speedy structured way. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19266
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| Posted: Sun Feb 28, 2016 10:31 am |
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Yes.
The internal pull-ups are 'OK' for non critical things like a keyboard, or inputs, where you do not read them till after you have setup the pull-ups, but 'beware' of using them for anything that requires a signal floats or is driven 'to' a level. They are very low current (which may not be enough to operate some circuitry), and the time before they are enabled, can be very dangerous.
It has always surprised me, that given the fuses like the one controlling the default ADC port selection on some chips, that MicroChip has never implemented a chip with a fuse controlled pull up/down. |
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gjs_rsdi
Joined: 06 Feb 2006
Posts: 468
Location: Bali
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| Posted: Sun May 29, 2016 11:54 pm |
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Same with the PIC16F1847
After spending a day searching the problem 
I read the data sheet:
| Quote: | 12.2.1 WEAK PULL-UPS
Each of the PORTA pins has an individually configurable
internal weak pull-up. Control bit WPUA<5> enables or
disables the pull-up (see Register 12-6). The weak
pull-up is automatically turned off when the port pin is
configured as an output. The pull-up is disabled on a
Power-on Reset by the WPUEN bit of the
OPTION_REG register.
REGISTER 12-6: WPUA: WEAK PULL-UP PORTA REGISTER |
only WPUA5 imlemented!!!
By the way the CCS Wizard letting me to chose Port A pull-ups!!!
The LST shows
| Code: | .................... port_a_pullups(0xC0);
007B: MOVLW C0
007C: MOVLB 04
007D: MOVWF WPUA
007E: MOVLB 01
007F: BCF OPTION_REG.WPUEN
.................... |
So I was thinking the pull-ups are enabled, but they are not there at all.
Ttelmah, regarding your sentence
| Quote: | | The internal pull-ups are 'OK' for non critical things like a keyboard, or inputs, where you do not read them till after you have setup the pull-ups |
I am reading some of port B pins with switches that are giving ground for '0' logic if ON. Do you think the internal pull-up's are OK for that?
I am reading them just in the main in the "while", the settings are the first line in the main:
| Code: | | port_b_pullups (0xFF); |
In the past I used always pull-ups, but I want to reduce components on the board
Best wishes
Joe |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19266
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| Posted: Mon May 30, 2016 1:17 am |
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Yes. Your 'switches' are effectively a 'keyboard'. Just happens to be using slightly more solid switches than most. 
However 'beware' that like any keyboard, 'bounce' is always potentially there. My keyboards always use a timer interrupt to scan, and don't accept they are 'on', till the same state is seen on two successive passes through the interrupt. |
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gjs_rsdi
Joined: 06 Feb 2006
Posts: 468
Location: Bali
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| Posted: Mon May 30, 2016 2:33 am |
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Thank you Ttelmah
In the specific program I am polling the switches, testing consecutive 8 times '1' or '0' logic.
Best wishes
Joe |
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