Heya,
I was reading the book: 8051 micrcontrollers, authir david calcutt and i am not sure about my understanding to section 1.8: Microcontroller clock. The author gave this code
under the assumption that
SETB takes 6 microcontroller clock cycles CLR takes 6 microcontroller clock cycles AJMP takes 12 microcontroller clock cycles JB takes 12 microcontroller clock cycles
the author concludes that SETB is held for 6 clock cycles and CLR is held for 30 clock cycles. the output waveform is shown in Figure 1.12:
+-------+-----+---------+-----------+-----+
..setB....CLR.....AJMP........JB..........setB
....6........6..........12...........12..........6
setB : for 6 cycles, the logic is one
CLR: for 6 cycles, the logic is zero
AJMP: for 12 cycles, the logic is zero
JB: FOR 12 cycles the logic is zero
SETB: for 6 cycles the logic is one
I want just to make sure i am getting the timing correct. I believe that the line will switch to logic 1 after the execution of setB to completion. Hence it will be one during the CLR instruction exection. it remains 1 until CLR finishes its operation. then it switches to 0 and remains at this level until the next instruction: AJMP finishes. this takes 12 cycles, then there is a jump to strt and execution of JB, THEN THE jump to PULSE label. the line won't get one until setB is completed. Hence we should have something like this:
+-------+---------+-----------+-----+-----+
...clr........AJMP ......JB...........setB....clr
....6............12........12............6.......6
CLR: for 6 cycles, the logic is one
AJMP: for 12 cycles, the logic is zero
JB: FOR 12 cycles the logic is zero
SETB: for 6 cycles the logic is zeru
clr : for 6 cycles, the logic is one
I know we end up having the same waveform cuz clr and setB consumes the same number of cycles but want to make sure i am getting the timing right. another question, what about when the change to the logic level occurs before the end of the last cycle, e.g. setb happens at clock cycle 4 as 4, and 5 are dummies. should we take care of this as well? I can't find the exact timing of the machine cycle of the different instructions
cheers
I was reading the book: 8051 micrcontrollers, authir david calcutt and i am not sure about my understanding to section 1.8: Microcontroller clock. The author gave this code
Code:
$INCLUDE (REG66X.INC) ; lists all sfr addresses
ORG 0 ; sets start address to 0
SJMP START ; short jump to START label
ORG 0040H ; putsnextprogram line at address 0040H
START: JB P1.0,PULSE ; jump to PULSE if pin 0, port 1 is logic 1
CLR P1.7 ; otherwise clear pin 7 port 1 to zero
SJMP START ; go to START check switch
PULSE: SETB P1.7 ; set pin 7 on port 1 to logic 1
CLR P1.7 ; clear pin 7 on port 1 to logic 0
AJMP START ; go to START check switch
END ; no more assembly languageSETB takes 6 microcontroller clock cycles CLR takes 6 microcontroller clock cycles AJMP takes 12 microcontroller clock cycles JB takes 12 microcontroller clock cycles
the author concludes that SETB is held for 6 clock cycles and CLR is held for 30 clock cycles. the output waveform is shown in Figure 1.12:
+-------+-----+---------+-----------+-----+
..setB....CLR.....AJMP........JB..........setB
....6........6..........12...........12..........6
setB : for 6 cycles, the logic is one
CLR: for 6 cycles, the logic is zero
AJMP: for 12 cycles, the logic is zero
JB: FOR 12 cycles the logic is zero
SETB: for 6 cycles the logic is one
I want just to make sure i am getting the timing correct. I believe that the line will switch to logic 1 after the execution of setB to completion. Hence it will be one during the CLR instruction exection. it remains 1 until CLR finishes its operation. then it switches to 0 and remains at this level until the next instruction: AJMP finishes. this takes 12 cycles, then there is a jump to strt and execution of JB, THEN THE jump to PULSE label. the line won't get one until setB is completed. Hence we should have something like this:
+-------+---------+-----------+-----+-----+
...clr........AJMP ......JB...........setB....clr
....6............12........12............6.......6
CLR: for 6 cycles, the logic is one
AJMP: for 12 cycles, the logic is zero
JB: FOR 12 cycles the logic is zero
SETB: for 6 cycles the logic is zeru
clr : for 6 cycles, the logic is one
I know we end up having the same waveform cuz clr and setB consumes the same number of cycles but want to make sure i am getting the timing right. another question, what about when the change to the logic level occurs before the end of the last cycle, e.g. setb happens at clock cycle 4 as 4, and 5 are dummies. should we take care of this as well? I can't find the exact timing of the machine cycle of the different instructions
cheers
