C868_02 Datasheet, PDF (164/244 Pages) Infineon Technologies AG – 8 - Bit CMOS Microcontroller

C868
On-Chip Peripheral Components
Sample Time t_S :
During this time the internal capacitor array is connected to the selected analog input
channel and is loaded with the analog voltage to be converted. The analog voltage is
internally fed to a voltage comparator. With beginning of the sample phase the BSY bit
in SFR ADCON0 is set.
Conversion Time t_CO :
During the conversion time the analog voltage is converted into a 8-bit digital value using
the successive approximation technique with a binary-weighted capacitor network.
During an A/D conversion also a calibration takes place. During this calibration
alternating offset and linearity calibration cycles are executed. At the end of the
calibration time the ADBSY bit is reset and the IADC bit in SFR IRCON1 is set indicating
an A/D converter interrupt condition.
Write Result Time t_WR :
At the result phase the conversion result is written into the ADDATH registers.
A/D Conversion Timing in Relation to Processor Cycles
Depending on the application, typically there are three methods to handle the A/D
conversion in the C868.
Software delay
The machine cycles of the A/D conversion are counted and the program executes a
software delay (e.g. NOPs) before reading the A/D conversion result in the write result
cycle. This is the fastest method to get the result of an A/D conversion.
Polling ADBSY bit
The ADBSY bit is polled and the program waits until ADBSY=0. Attention : a polling JB
instruction which is two machine cycles long, possibly may not recognize the ADBSY=0
condition during the write result cycle in the continuous conversion mode.
A/D conversion interrupt
After the start of an A/D conversion the A/D converter interrupt is enabled. The result of
the A/D conversion is read in the interrupt service routine. If other C868 interrupts are
enabled, the interrupt latency must be regarded. Therefore, this software method is the
slowest method to get the result of an A/D conversion.
User’s Manual
4-120
V 0.4, 2002-01