COP8CBR9 National Semiconductor, COP8CBR9 Datasheet - Page 54

• Manufacturer Part Number: COP8CBR9
• Description: 8-Bit CMOS Flash Microcontroller with 32k Memory/ Virtual EEPROM/ 10-Bit A/D and Brownout
• Manufacturer: National Semiconductor

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15.0 A/D Converter
15.1.1.3 Mode Select
This 1-bit field is used to select the mode of operation (single
ended or differential) as shown in the following Table 22.
15.1.1.4 Prescaler Select
This 1-bit field is used to select one of two prescaler clocks
for the A/D Converter. The following Table 23 shows the
various prescaler options. Care must be taken, when select-
ing this bit, to keep the A/D clock frequency within the
specified range.
15.1.1.5 Busy Bit
The ADBSY bit of the ENAD register is used to control
starting and stopping of the A/D conversion. When ADBSY is
cleared, the prescale logic is disabled and the A/D clock is
turned off, drawing minimal power. Setting the ADBSY bit
starts the A/D clock and initiates a conversion based on the
TABLE 22. A/D Conversion Mode Selection
TABLE 23. A/D Converter Clock Prescale
ADMOD
PSC
0
1
0
1
FIGURE 26. A/D with Single Ended Mux Output Feature Enabled
FIGURE 27. A/D with Differential Mux Output Feature Enabled
(Continued)
Single Ended Mode
MCLK Divide by 16
MCLK Divide by 1
Differential Mode
Clock Select
Mode
54
values currently in the ENAD register. Normal completion of
an A/D conversion clears the ADBSY bit and turns off the A/D
Converter.
If the user wishes to restart a conversion which is already in
progress, this can be accomplished only by writing a zero to
the ADBSY bit to stop the current conversion and then by
writing a one to ADBSY to start a new conversion. This can
be done in two consecutive instructions.
15.1.2 A/D Result Registers
There are two result registers for the A/D converter: the high
8 bits of the result and the low 2-bits of the result. The format
of these registers is shown in Figures 27, 28. Both registers
are read/write registers, but in normal operation, the hard-
ware writes the value into the register when the conversion is
complete and the software reads the value. Both registers
are undefined upon Reset. They hold the previous value until
a new conversion overwrites them. When reading ADRSTL,
bits 5-0 will read as 0.
Bit 7
Bit 7
Bit 9
Bit 1
Bit 8
Bit 0
Bit 7
0
10137429
TABLE 24. ADRSTH
TABLE 25. ADRSTL
10137430
Bit 6
0
Bit 5
0
Bit 4
0
Bit 3
0
Bit 0
Bit 0
Bit 2
0