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Processing explanation of Transmitter

Environment setting Various environment setting is done at the line number 008-011 of the list.
    008
    list
| It is defining the name of PIC to use.
    009
    include
| The file (p16f84a.inc) that a various standard label is defined is taken in.
    010
    __config
| The contents of Configuration Word are designated.
| _hs_osc |  | Type of the oscillator | : HS
_wdt_off | Watch-dog timer | : It isn't used.
_pwrte_on | Power up timer | : It is used.
_cp_off | Code protector | : It isn't used.
The value of Configuration Word by above-mentioned specification is H'3FF2'.
    011
    errorlevel
| It makes not show bank switching warning message [302]. At the RAM file register of PIC16F84A, a bank method is adopted. For example, both memory addresses of TMR0 and OPTION_REG is 01. However, TMR0 is at bank 0 and OPTION_REG is at bank 1. In the definition file which is read by INCLUDE, it defines the address of OPTION_REG as being H'0081'. Bank information is written. The bank must be designated with RP0 bit of the STATUS register by the actual processing. In case of MPLAB, to prevent mistake in the bank processing, warning message "Message[302]" is shown in the processing of the register of bank 1. "Register in operand not in bank 0. Ensure that bank bits are correct." Even if specifying a bank normally, this message is shown. To make not display this message, there is a way of changing a definition file designation. That is, the message becomes not displayed when changing the address of OPTION_REG into H'0001'. Or, there is a way of stopping the display of 302 messages using the ERRORLEVEL directive to be using this time.
Label definition
    ;****************  Label Definition  ********************
CBLOCK and ENDC are used for the block definition of the RAM register file. The area of the label among these commands is automatically set in the order from the address which is specified by CBLOCK. This time, it is the same as specifying as follows.
    tx_status     equ    h'000c'
    tx_substatus  equ    h'000d'
    pattern       equ    h'000e'
ptn1 and ptn2 are the label which specifies control code data. If changing the value to specify here, the control code to transmit can be changed. In the case, the side of the receiver must be changed too. ra4 is the label which specifies the position of port A. "4" can be designated to direct by the instruction even if it doesn't use ra4, too. Program start
    ;**************** Program Start ***********************
The program memory address 0 is the program starting address when turning on or reset occurs. Also, the program memory address 4 is a start address when interruption occurs. These addresses are decided with the hardware of PIC16F series. Initialization process
    ;****************  Initial Process  *********************
Port initialization First, the initialization of the port is done. RA0 and RA1 are set to the input mode and the other RA ports which contain RA4 are set to the output mode. Timer setting This circuit controls the data to transmit in the 10-millisecond interval. Timer 0 is used to make 10-millisecond time. TOCS and PSA of OPTION_REG are set to "0" to use an internal clock and prescaler for timer 0. It makes prescaler value "101"(1:64). Because it is using 4 MHz for the oscillator of PIC, the clock is one microsecond. TMR0 is increased every 64 microseconds when combining with prescaler. The timer interrupt generates TMR0 when count value (TMR0) becomes 0 from 255(H'FF'). So, the value to set to TMR0 for the 10-millisecond timer is 256-(10000/64)=100. The other value can be used for the prescaler value. In case of 1:128, the timer increases every 128 microseconds. In the case, the set value of TMR0 is 256-(10000/128)=178. In case of 1:256, it is 256-(10000/256)=217. When the prescaler value is small, the timer value by TMR0 can be set, being detailed. However, in case of 1:32, it becomes 10000/32=312.5. The value more than 255 can not be set to TMR0. Initialization of the register When turning on the power of PIC, the initialization for various register is executed with hardware. I am doing initialization to make those original values certainty. Confirmation of the transmission pattern It checks the condition of RA0 and RA1 and it confirms a transmission pattern. RA0 becomes an H level when SW1 is pushed and RA1 becomes an H level when SW2 is pushed. By the condition of the pushed switch, a control code pattern is set to the PATTERN register. When SW1 and SW2 are pushed at the same time, SW1 is judged to have been pushed. Timer interrupt wait After above processing, it waits for the interruption of the timer only. It specifies $ (its address) by the GOTO instruction, and it repeats the processing of the same address and it waits for the interruption. Timer interrupt process
    ;*********  Begin Timer Interruption Process  ***********
In the processing this time, the interruption has only a timer time-out. So, it assumes that all interruption is a timer interrupt. When using the other interruption (the RB port change interruption, and so on), judgment processing of the interruption factor is needed. First, it clears a timer interrupt flag. When not clearing this, the timer interrupt occurs again immediately after executing interruption ending instruction (RETFIE). Preamble data sending-out process
    ;************  Preamble data send Process  **************
When transmission status (TX_STATUS) is "0", it sends out a preamble signal. It transmits ON and OFF three times alternately and making do continuously ON in twice in case of transmission ending. After transmitting the end mark, it makes an electric wave OFF and it ends in the sending-out of a preamble signal and it makes transmission status "1". Control code data sending-out process
    ;************  Control data send Process  ***************
When the transmission status is "1", the sending-out processing of a control code is done. It sends ON signal in front of each bit of the control code and it sends OFF signal back. The condition of the sending-out bit is managed by sub status (TX_SUBSTATUS). I think that it is possible for more few processing steps to realize if devising processing. However, I made the processing of each signal to be independent. The quantity consumed of the program memory increases but can make an execution time little. It is because there are not judgement processing and so on too much. This time, because the program is small, the memory is enough. Also, in this way, the understanding of processing is easy and there is little possibility to make bug (the mistake of the software). It makes transmission status "2" when the sending-out of a control code ends. Ending data sending-out process
    ;**************  End data send Process  *****************
When the transmission status is "2", the sending-out processing of an ending code is done. The ending code continues ON condition three times and makes it OFF condition last. By making transmission status "0" after finishing transmitting an ending code, the transmission of the preamble is again done. Timer interrupt ending process
    ;***********  Substatus Increment Process  **************

    ;********  End of Timer Interruption Process  ***********
A timer interrupt is done every 10 milliseconds and code transmission processing is done by the contents of the transmission status and the transmission sub status. When the timer interrupt processing ends, it sets 10 milliseconds to timer value (TMR0) and it sets a timer interrupt condition for next time. Depending on the condition of the status, sub status is sometimes increased. The interruption processing ends using the RETFIE instruction. With this instruction, the GIE bit of the INTCON register becomes "1" and the interruption becomes possible.