HD404654 Datasheet, PDF (86/111 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404654 Series
Comparator
The block diagram of the comparator is shown in figure 71. The comparator compares input voltage with
the reference voltage.
Setting 1 to bit 3 (CER3) of the compare enable register (CER: $018) executes a voltage comparison. If an
input voltage at COMP₀ or COMP₁ is higher than the reference voltage, the TM or TMD command sets the
status flag (ST) high for the corresponding bits of the compare data register (CDR: $017) to COMP₀ or
COMP₁. On the other hand, if an input voltage at COMP₀ or COMP₁ is lower than the reference voltage,
the TM or TMD command clears the ST to 0.
COMP₀
COMP₁
VC_ref
+
Com-
parator
–
Comparator data
register (CDR)
2
Comparator enable
register (CER)
Figure 71 Block Diagram of Comparator
Compare Enable Register (CER: $018): Three-bit write-only register which enables comparator
operation, and selects the reference voltage and the analog input pin.
Compare Data Register (CDR: $017): Two-bit read-only register which latches the result of the
comparison between the analog input pins and the reference voltage. Bits 0 and 1 reflect the results of
comparison with COMP₀ and COMP₁, respectively. This register can be read only by the TM or TMD
command. Only bit CER3 corresponds to the analog input pin, which is selected by bits CER0 and CER1.
After a compare operation, the data in this register is not retained.
Note on Use: During compare operation, pins RD₀/COMP₀ and RD₁/COMP₁ operate as analog inputs and
cannot operate as R ports.
The comparator can operate in active mode but is disabled in other modes.
RE₀/VC_ref cannot operate as an R port when the external input voltage is selected as the reference.
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