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'[PIC]: 16F84A + External TLC548CP ADC, Will it wor'
2001\11\02@010506 by Dylan Hillier

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I hate to ask questions that have probably been asked a thousand times
before but.....

I have a PIC16F84A and a texas intruments TLC548CP 8 Bit Serial Analog to
Digital Converter.
What i would like to know is if i can use them together, ie read values
from the ADC and
store them in EEPROM temporarily before processing them later.

I am ofcourse a newbie and have limited knowledge in the use of such
devices and am
a little confused when the data sheet says something like:

I/O Clock is 2.048Mhz
Internal System Clock is Typically 4Mhz

Then it goes on to say "...for flexibility and access speed, there are two
control inputs: I/O Clock and Chip Select."

Hrmmm... does this mean it only requires the external clock if using the
I/O clock as a control input and i can still
get samples from the ADC by only holding CS high or low for x amount of uS
even if i dont provide an external clock ?


Then there is the problem of actually reading the sample as its output
quick enough by the Pic controller to get
the right conversion information... from what i gather the following is
almost correct:

; bring CS low for 2 clock cycles ( 1.4 uS ) NOTE: CS is inverted.
; wait 8 clock cycles for conversion to take place. (5.6 uS )
; bring CS high for conversion cycle   ( 8uS normal, 17uS max )
; wait for output to be enabled ( 1.4 uS Max )
; read data pint every uS to get data
; shift this information left onto a GPR
; read next bit

I can see problems in that the clock cycle for this appears to be about
0.7uS and  the pic only
executres 1 instruction every 1uS.

Is it possibly to safely underclock this ADC so that it will run at system
clock period of of 2us?

Another thought i have (again not sure if its even valid with my newbie
knowledge) is with the use of a
shift register thats operating at the same frequency as the ADC. Using the
PIC to enable/start the conversion
cycle as well as to enable the shift register. Then read the 8 bits from
the shift register using port B.

Im tempted to use another ADC i have, an 8 channel 10 bit covnerter with
all sorts of fancy functions but the bloody thing is
surface mount package making it near impossible to experiment with.



Dylan.

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