serin/hserin fail when i break the standard...

[Melanie]

If you have a Hardware COMPARATOR on the PIC, put your 3v SERIAL into one pin, set a low voltage Reference - say around 1v-2v (using the conveniently provided Voltage Reference Module of the PIC), and cross-connect the Hardware OUTPUT of the Comparator to either your USART input on the PIC or your chosen PIC pin for ASYNC Comms.

Hey presto... you have your very own personal Voltage Convertor... and other than the software initialisation at the start of your program, no further software is required - so won't affect any critical timekeeping or interrupts or anything.

What's even better, you can INVERT the Comparators output simply in SOFTWARE by setting the appropriate Register Bit... so you also have your own programmable HARDWARE INVERTOR... throw your MAX232 in the bin - your PIC (if it has Comparators) has one BUILT IN!!!!

And if anyone is still using MAX232's for INPUT to a PIC... why??? The chances are if your PIC has a USART (like the 16F628), then it's probably got COMPARATORS too... so use them!

Remember... your COMPARATOR's OUTPUT will swing 0v-Vdd (ie 0-5v on a 5v PIC) as long as the INPUT to the comparator reaches or exceeds the REFERENCE VOLTAGE. So if you have SERIAL Comms at say 15mV out of a Radio Receiver... feed it STRAIGHT into your Comparator, set the Reference to 10mV and suddenly you've got an amplified 0-5v SERIAL appearing on the Comparators Hardware OUTPUT pin.

C'mon... if you've got a COMPARATOR you can rule the world!!!....

[Pic2008]

Melanie, I thought RS232 required negative voltage eg -12V? All this while I thought MAX232 is needed to generate +12V and -12V for the signalling.

[Melanie]

You can connect a PIC directly to RS232 (usually though a Resistor). The problem is YES it is inverted. For all intents and purposes a HIGH (say +12v) is ZERO, and a low (-12v) is a ONE. You can extend this by simply saying, that if it isn't a HIGH, then it's got to be a LOW. So again, if the signal is above 5v (ie it has swung to +12) the PIC will tollerate that (our Resistor helps) and Register a PIC LOGIC 1 (RS232=Zero), and if the swing goes to -12v, again our PIC doesn't care once it falls below 0v, because it registers a Logic 0 (RS232=1). So here +12/-12v is fine, just a Resistor and you're good to go.

If you use SOFTWARE ASYNC like SERIN, you do it simply by specifying that it is inverted and SERIN does the rest.

But if you use the HARDWARE USART, and HSERIN, there is no automatic way of inverting, so you need something like a MAX232 (or transistor or whatever) to HARDWARE INVERT the signal before you feed it into the PICs USART.

In this thread a 0v to +3v swing doesn't do it for the PIC running at 5v. 3v may or may not be sufficient to score a Logic 1 in the PIC. It's unreliable, and it looks like f-lez has a problem. But here is where the Comparator scores on TWO COUNTS. (1) it can RESTORE your 0-5v signal (from an input as little as only a few millivolts), and (2) it has the ability to INVERT the output for you (real convenient when you need to INVERT a signal for the USART).

The COMPARATOR won't give you +12/-12v for OUTPUT purposes, but it will take whatever cr*p you want to throw at it and give you clean Data with a nice solid 0-Vdd swing for the PIC to logically process thereafter. So treat the COMPARATOR as a LOGIC LEVEL SHIFTER, a DATA RESTORER, an INVERTOR, an AMPLIFYER, a NOISE FILTER... what more could you ask for? And you got it FREE all BUILT-IN to your PIC!

[ScaleRobotics]

But if you use the HARDWARE USART, and HSERIN, there is no automatic way of inverting, so you need something like a MAX232 (or transistor or whatever) to HARDWARE INVERT the signal before you feed it into the PICs USART.

Except for the PIC18 chips by using RXDTP and TXCKP to invert your hardware UART.

See

http://www.picbasic.co.uk/forum/show...ight=inverting

By the way Melanie, your comparator solution is very slick! Thanks, I have a 3v to 5 volt issue I think I will use it on.

Thanks,

Walter

[Bruce]

A lot of people miss this, but if you have an external 3V device, and it's not working on a
certain pin, make sure you're not using a pin with a Schmitt Trigger input buffer.

A pin with a TTL input buffer should work fine with the 3V input if VDD >= 4.5V and <= 5.5V.

A Schmitt Trigger input needs ~0.8 * VDD to meet the input logic 1 threshold.

The comparator trick is cool too, but you might fix it by just switching to a TTL input.

[f_lez]

Ha ha some good ideas i like the comparator hack, i may have to try that as a test to see just if it is a level issue, as i would like to keep those pins free for the pwm.

Pic is 18f2550 so it has them, and I am running it at 5v, the phone/dsm module is 3v but 5v wont harm it.

I have tried input on both port b and C and tried with and without pullups enabled.

I will try the HW uart again with inverted as i am unsure of the stream polarity.

Heres the start of my code as a test etc and to show the configs I have

;DEFINE RESET_ORG 800h 
;DEFINE INTERRUPT_ORG 808h 

define OSC 48
;dEFINE LOADER_USED 1


 ; first four lines to fix broken pbp246
UIR  VAR BYTE EXT
UIE  VAR BYTE EXT
UEIE VAR BYTE EXT
UEIR VAR BYTE EXT


INCLUDE "MODEDEFS.BAS"


include "c:\dtusbsvc.pbp"  ' would not know what to do without them !

' setup serial hardware comms 

DEFINE HSER_RCSTA	90h
DEFINE HSER_TXSTA	20h    ; try 24 if errors
DEFINE HSER_BAUD	9600
DEFINE HSER_EVEN	1
DEFINE CHAR_PACING 1000   ' slow things a little
DEFINE HSER_CLOERR  1 ' automatic clear overrun error

' DEFINE HSER_SPBRG	25  ' let picbasic set it from the baud def above




DEFINE ADC_CLOCK 1
DEFINE ADC_BITS 8
DEFINE ADC_SAMPLEUS 10

ADCON1 = %10000011 ; not sure lol
CMCON = 7                 ' Disable Comparators
INTCON2.7 = 0 ; should enable portb pullups.


TRISA = 3      ;  configure AN0 an1 as an input 
trisb = 255
trisc=255

tempx     var byte ; temps..
tempy     var byte ; temps..

loop:

hserout ["atd123",13,10]

for tempx=1 to 2 ; look for 2 chars from it for ''ok''

serin portb.7,n9600,10,tlable,tempy
tlable:

; gosub send tempy to usb to pc terminal

next

goto loop

[Bruce]

What do you get with: serin portb.7,T9600,tempx,tempy