Status: Assigned
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 170 by [email protected]: 16f33 HiRes ADC
http://code.google.com/p/jallib/issues/detail?id=170
I have a problem trying to read the highest 2 bits of the ADC.
The following program will reproduce the problem
---------------------------------------------------------------------
include 16f1933 -- target PICmicro
--
pragma target clock 16_000_000 -- oscillator frequency
pragma target OSC INTOSC_NOCLKOUT --
pragma target PLLEN P1 -- PLL off
--
OSCCON_SPLLEN = 0 -- PLL off
OSCCON_IRCF = 0b1111 -- 16 MHz
OSCCON_SCS = 0b00 -- fuses determine clock source
--
pragma target WDT disabled -- no watchdog
pragma target DEBUG disabled -- no debugging
pragma target LVP disabled -- no Low Voltage Programming
pragma target MCLR external -- reset externally
--
enable_digital_io() -- make all pins digital I/O
-- ---------------
-- configure ADC
-- ---------------
const bit ADC_HIGH_RESOLUTION = true
const byte ADC_NVREF = ADC_NO_EXT_VREF
include adc
adc_init()
set_analog_pin(10)
set_analog_pin(12)
-- ---------------
-- setup i2c slave
-- ---------------
const byte I2C_BUFFER_SIZE = 5
include i2c_hw_slave_msg
const byte SLAVE_ADDRESS = 0x5C
i2c_hw_slave_init(SLAVE_ADDRESS)
-- ------------------------------------------------
-- i2c_process_message - User code for i2c slave
procedure i2c_process_message(byte in byte_count) is
var byte mHi
var byte mLo
if (i2c_buffer[0] == 0x20) then
if (byte_count == 2) then
if (i2c_buffer[1] == 0) then
adc_read_bytes(10,mLo,mHi)
i2c_buffer[0] = mHi
i2c_buffer[1] = mLo
end if
end if
end if
end procedure
var word measureHiRes
measureHiRes = adc_read(12)
forever loop
end loop
---------------------------------------------------------------------
What is the expected output? What do you see instead?
If I remove the "measureHiRes = adc_read(12)" before the forever loop
I will get the expected output when I poll the value via I2C (all 10 bits)
adding the "measureHiRes = adc_read(12)" to read an ADC channel outside the
ISR will corrupt the higher 2 bits returning, in this case, 0x78 instead.
If I change things to only do 8 bit resolution the program works as expected
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