C517A_99 Datasheet, PDF (167/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C517A
conversion also a calibration takes place. During this calibration alternating offset and linearity
calibration cycles are executed (see also section 6.6.5). At the end of the conversion time the BSY
bit is reset and the IADC bit in SFR IRCON0 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 ADDAT registers.
Figure 6-45 shows how an A/D conversion is embedded into the microcontroller cycle scheme
using the relation 12 x t _IN = 1 instruction cycle. It also shows the behaviour of the busy flag (BSY)
and the interrupt flag (IADC) during an A/D conversion.
Prescaler
Selection
MOV ADDATL,
#0
1 Instruction Cycle
Write Result Cycle
MOV A, ADDATL
ADCL = 0
X-1 X 1 2 3 4 5 6 7 8 9 10 11 12
ADCL = 1
X-1 X 1 2 3 4 5
Start of A / D
conversion Cycle
t _ADCC
15 16 17 18 19 20
Start of next conversion
(in continuous mode)
BSY Bit
A / D Conversion Cycle
Write
ADDAT
Cont. conv.
Single conv.
ADCL = 0 _{IADC Bit}
ADCL = 1 _{IADC Bit}
First Instr. of an
Interrupt Routine
First Instr. of an
Interrupt Routine
MCT03266
Figure 6-45
A/D Conversion Timing in Relation to Processor Cycles
Depending on the selected prescaler ratio (see figure 6-43), two different relationships between
machine cycles and A/D conversion are possible. The A/D conversion is always started with the
beginning of a processor cycle when it has been started by writing SFR ADDATL with dummy data
or after an high-to-low transition has been detcted at P6.0 / ADST. The ADDATL write operation
may take one or two machine cycles. In figure 6-45, the instruction MOV ADDATL,#00 starts the
A/D conversion (machine cycle X-1 and X). The total A/D conversion is finished with the end of the
8th or 16th machine cycle after the A/D conversion start. In the next machine cycle the conversion
result is written into the ADDAT registers and can be read in the same cycle by an instruction (e.g.
Semiconductor Group
6-101