C8051F336/7/8/9
9.1.2. Update Output Based on Timer Overflow
Similar to the ADC operation, in which an ADC conversion can be initiated by a timer overflow indepen-
dently of the processor, the IDAC outputs can use a Timer overflow to schedule an output update event.
This feature is useful in systems where the IDAC is used to generate a waveform of a defined sampling
rate by eliminating the effects of variable interrupt latency and instruction execution on the timing of the
IDAC output. When the IDA0CM bits (IDA0CN.[6:4]) are set to ‘000’, ‘001’, ‘010’ or ‘011’, writes to both
IDAC data registers (IDA0L and IDA0H) are held until an associated Timer overflow event (Timer 0,
Timer 1, Timer 2 or Timer 3, respectively) occurs, at which time the IDA0H:IDA0L contents are copied to
the IDAC input latches, allowing the IDAC output to change to the new value.
9.1.3. Update Output Based on CNVSTR Edge
The IDAC output can also be configured to update on a rising edge, falling edge, or both edges of the
external CNVSTR signal. When the IDA0CM bits (IDA0CN.[6:4]) are set to ‘100’, ‘101’, or ‘110’, writes to
both IDAC data registers (IDA0L and IDA0H) are held until an edge occurs on the CNVSTR input pin. The
particular setting of the IDA0CM bits determines whether IDAC outputs are updated on rising, falling, or
both edges of CNVSTR. When a corresponding edge occurs, the IDA0H:IDA0L contents are copied to the
IDAC input latches, allowing the IDAC output to change to the new value.
9.2. IDAC Output Mapping
The IDAC data registers (IDA0H and IDA0L) are left-justified, meaning that the eight MSBs of the IDAC
output word are mapped to bits 7–0 of the IDA0H register, and the two LSBs of the IDAC output word are
mapped to bits 7 and 6 of the IDA0L register. The data word mapping for the IDAC is shown in Figure 9.2.
IDA0H
IDA0L
IDA09 IDA08 IDA07 IDA06 IDA05 IDA04 IDA03 IDA02 IDA01 IDA00
Input Data Word
(IDA09–IDA00)
0x000
Output Current
IDA0OMD[1:0] = ‘1x’
0 mA
Output Current
IDA0OMD[1:0] = ‘01’
0 mA
Output Current
IDA0OMD[1:0] = ‘00’
0 mA
0x001
0x200
0x3FF
1/1024 x 2 mA
512/1024 x 2 mA
1023/1024 x 2 mA
1/1024 x 1 mA
512/1024 x 1 mA
1023/1024 x 1 mA
1/1024 x 0.5 mA
512/1024 x 0.5 mA
1023/1024 x 0.5 mA
Figure 9.2. IDA0 Data Word Mapping
The full-scale output current of the IDAC is selected using the IDA0OMD bits (IDA0CN[1:0]). By default,
the IDAC is set to a full-scale output current of 2 mA. The IDA0OMD bits can also be configured to provide
full-scale output currents of 1 mA or 0.5 mA, as shown in SFR Definition 9.1.
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