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wcgan
Joined: 01 Nov 2006
Posts: 38
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 06 Oct 2008 6:51 some basic PIC microcontroller question..need your help |
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Hi all,
I am fresh to PIC controller, i hv some basic microcontroller question need you help..
Question 1:Memory Size:
For 8051, datasheet written
- 128 x 8-bit Internal RAM
is that means 1 memory location can store 8-bits data. total hv 128 memory location, so the total memory RAM size is
128 x 8 bits = 1024 bits
128 x 1 byte = 128bytes
is that the same calcucaltion theory can apply to PIC controller?
from PIC16F876 datasheet,
Up to 8K x 14 words of FLASH Program Memory,
Up to 368 x 8 bytes of Data Memory (RAM)
Up to 256 x 8 bytes of EEPROM Data Memory
is that means 1 memory location can store 8-bytes data, total hv 368 memory location, so the total memory size is
#cal1
368 x 8 x 8 bits = 23552 bits
368 x 8 bytes = 2944 bytes
OR
#cal2
368 x 8 bits = 2944 bits
368 x 1 byte = 368 bytes
which calculation is correct? if cal2 is correct, y the unit display on datasheet is 'bytes' NOT 'bits'?
Up to 368 x 8 bits of Data Memory (RAM)
is that the standard display way for the microcontroller?
Up to 8K x 14 words of FLASH Program Memory
1 words = 4 bytes
8k x 14 words = 8k (memory location) x (14 x 4) = 448000 bytes?
Question 2:14-bits op-code vs. 8-bits op-code:
what means of 14-bits op-code? what r the different between 8 bits op-code?
is that means they can do more task on one command?
example:
A = 0x05 + 0x09;
in 8051,(8-bits op-code)
ADD A,#05H
ADD A,#09H
in PIC,(16-bits op-code)
ADD A,#05H,#09H
16-bits op-code can done the job on one 'ADD' command?
Thanks for your help.
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penoy_balut
Joined: 08 Sep 2007
Posts: 129
Helped: 16
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| 06 Oct 2008 7:14 some basic PIC microcontroller question..need your help |
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#1, ram is counted in bytes not bits
#2, PIC has paging and banking that's why it has extra bits in its op code to switch between banks or pages
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wcgan
Joined: 01 Nov 2006
Posts: 38
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| 06 Oct 2008 7:23 Re: some basic PIC microcontroller question..need your help |
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| penoy_balut wrote: |
#1, ram is counted in bytes not bits
#2, PIC has paging and banking that's why it has extra bits in its op code to switch between banks or pages |
sorry, i am not understand yet.
u mentions ram is counted in bytes. is that means PIC16F876A total RAM size r 2944 bytes?
368 x 8 bytes = 2944 bytes
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penoy_balut
Joined: 08 Sep 2007
Posts: 129
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| 06 Oct 2008 7:27 some basic PIC microcontroller question..need your help |
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| 368 x 8 means 368 registers of 8 bit data, that is for 8-bit microcontroller
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wcgan
Joined: 01 Nov 2006
Posts: 38
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| 06 Oct 2008 7:44 Re: some basic PIC microcontroller question..need your help |
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| penoy_balut wrote: |
| 368 x 8 means 368 registers of 8 bit data, that is for 8-bit microcontroller |
because the PIC16F876 datasheed showing that
368 x 8 bytes,after the 8 following with 'bytes' not 'bits', so i confuse on the number of 8 is represent of 'bit' or 'byte'.
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penoy_balut
Joined: 08 Sep 2007
Posts: 129
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| 06 Oct 2008 8:09 some basic PIC microcontroller question..need your help |
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| if that's a 16-bit microcontroller it could have been written as 368 x 16
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wcgan
Joined: 01 Nov 2006
Posts: 38
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| 06 Oct 2008 9:25 Re: some basic PIC microcontroller question..need your help |
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thanks. i understand the memory size already.
but i still cant understand wat r the different between
14-bits op-code vs. 8-bits op-code...
hope you can give me a sample on it.. thanks a lot.
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penoy_balut
Joined: 08 Sep 2007
Posts: 129
Helped: 16
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| 06 Oct 2008 9:58 some basic PIC microcontroller question..need your help |
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| programming PIC as a beginner does not require the knowledge about op code, familiarize yourself in its instruction sets, register addressing, banking and paging, after that you'll know how op code works
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wcgan
Joined: 01 Nov 2006
Posts: 38
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| 14 Oct 2008 1:54 Re: some basic PIC microcontroller question..need your help |
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[ SPI Clock Problem ]
Hi ,
I would like to generate 500k SPI clock with external crystal 4Mhz.
from datasheet, SPI clock have 4 modes(SSPCON)
0000 = SPI Master mode, clock = FOSC/4
0001 = SPI Master mode, clock = FOSC/16
0010 = SPI Master mode, clock = FOSC/64
0011 = SPI Master mode, clock = TMR2 output/2
SCK = 1Mhz (FOSC/4, with crystal 4Mhz)
SCK = 250khz (FOSC/16, with crystal 4Mhz)
the first 3 modes cant fullfill my requirment to generate 500khz.
Only mode 4 can customize the frequency, TMR2 output / 2.
my settings was shown below:
//SPI Settings
SSPIE = 0;
SSPEN = 0 ;
SSPSTAT= 0b11000000 ;
SSPCON = 0b00010011 ; // using mode 4
CKP = 1 ;
CKE = 0 ;
SMP = 1 ;
SSPEN = 1 ;
// Timer2 Settings
TOUTPS3 = 0; // Post Scaler = 1
TOUTPS2 = 0; //
TOUTPS1 = 0; //
TOUTPS0 = 0; //
T2CKPS1 = 0; // Prescaler = 1
T2CKPS0 = 0; //
TMR2 = 0;
PR2 = 1;
TMR2IE = 0;
PEIE = 0;
GIE = 0;
TMR2ON = 1;
Calculation:
Timer2 Clock Prescale Select bits = 1:1
FOSC = 4Mhz
FOSC/4 = 1Mhz(1us)
TMR2=0, PR2=1
TMR2 Output = 1Mhz (1us)
SPI
Synchronous Serial Port Mode Select bits = TMR2 output/2
= 1Mhz / 2
= 500khz(2us)
But i probe SCK pin from osillacscope, the frequency is 250khz (4us), anything goes wrong in my settings or wrong calculation?
Thanks.
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wcgan
Joined: 01 Nov 2006
Posts: 38
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| 15 Oct 2008 3:25 Re: some basic PIC microcontroller question..need your help |
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thanks..
i found out the reason.
TMR2 output = (4 / FOSC) x N x (PR2 + 1)
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