I cant figure out what the issue is. Super Member. A common cause of such problems is that you are not initializing a file register which you later rely on.
Remember that at power-up, most file registers contain random values many of the bits have the values they last had when power was previously applied, but you can't rely in this. Do not assume they start at zero. Exceptions to this rule are explicitly documented in the data sheet for your PIC. When the timing is "off", is it consistently off by the same amount? By what percentage? Such information is often helpful in tracking down the problem. If your source-code does not specify the oscillator configuration but instead you rely on the MPLAB IDE to set the config bits, it could be that you sometimes forget to set them before hitting "program".
Hope this helps, Danish. If you are using the internal oscillator for serial timing, you cannot expect the timing to be close enough for reliable serial communication. Even using the factory OSCCAL setting, the frequency still varies enough to cause problems, especially over the full range of Vcc and temperature. It might be possible to customize the timing for each chip, in your circuit.
But that would require an extra step in your build process to test the actual frequency of each chip and program the serial timing accordingly. And even then you might have problems if the Vcc or temperature change a lot from what they were when you tested. I hear that the internal oscillator is not good for serial communication but when I developed the app I had no issues. Now that could have just been lucky that the one chip I used worked, but I doubt it.
My code for serial communication is simple also. It simply sets pin x high, then pauses for us, then pin x low, pauses for us, etc.
Its nothing fancy and is working great, just not on all chips. Could it really be the oscillator is not good enough or is that just a theory i keep hearing? I will look into the file register issue. Let me get the more info you think will help. From memory it did seem that is was consistently off for each chip. IE, the data coming back from the chip was consistant, just off from what it should be.
Doesnt it have to vary between chips? I went through the same steps as you, fine tuning to get reliable serial communication on one 12F chip, then finding that every new chip I tried had to be calibrated differently. Even when I acheived what I thought was reliable communication, I would come back a few days later and find occasional errors on some PICs.
PIC12F seems so far to be much easier to work with. The oscillator is factory calibrated and is more accurate in absolute terms, as well as having less drift. I see mentions of improving accuracy by regular calibration using incoming serial data as a standard, but this seems like too much messing about to me. For reliable serial communication I use a resonator or a crystal clock. Loses 2 pins, but it takes away a lot of headaches. Just my opinion and my hobby experience. The oscillator will be off frequency if you aren't doing that.
Could it really be the oscillator is not good enough or is that just a theory i keep hearing?.. There is no need to guess.
Don't you have a scope? Leon No I am not doing this. I didnt read that this was necessary and I figured that when configured to use the internal oscillator it owuld just use the calibration value. This standard fixes the problem of few connected devices in RSA. RS is forward compatible standard with RSA. In RSC, the connectors to use and the signal assignments have been defined and are standardized.
The figure to the right describes the D-sub 9-pin signal assignments and signal lines. In RSC, the connectors and signal assignments have been standardized, so many standard-compliant cables are available commercially.
However, equipment comes in the following types, and depending on the equipment that will be connected, a straight cable or a crossover cable is required. Data communication equipment. This term indicates equipment that passively operates such as modems, printers, and plotters. In serial communication, data is sent one bit at a time using one signal line, so in order for the receiving side to accurately receive the data, the sending side must know at what speed it is sending each bit.
In RSC, synchronous communication and asynchronous communication standards have been defined. The most recent version of the protocol is known as RSC. RSC retains the features of RS but uses 25 pins rather than a 9 pin serial pinout. Whether a DB9 serial pinout or a 25 pin connection is used, only three of the pins are required to connect terminal devices.
Each pin in a 9 or 25 serial connector pinout has its own distinct function. You can also learn RS pinout. In addition to defining electrical characteristics, RS specifies the signals used in serial cable pinouts and serial ports. Familiar items such as timing signals and ground are included in these specifications. Protective Ground -This signal is connected to the chassis ground of the metallic connector.
These signals are the primary RS signals, but the protocol allows for secondary signals as well. Using the RS protocol you can connect two computers that do not have modems by using a null modem cable. This highlights one of the original uses of the RS protocol, which was developed in order to let teletype machines communicate with each other through their modems. The other type of RS Cable is the Straight-through cable. It is a one to one connector, It transmits a pin of one device that is connected to the transmit pin of another device and the receiver pin of one device is connected to the receiver pin of another device.
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