Datasheet

42
AT89C51ID2
4289C–8051–11/05
Table 27. CMOD Register
CMOD - PCA Counter Mode Register (D9h)
Reset Value = 00XX X000b
Not bit addressable
The CMOD register includes three additional bits associated with the PCA (See
Figure 14 and Table 27).
• The CIDL bit which allows the PCA to stop during idle mode.
• The WDTE bit which enables or disables the watchdog function on module 4.
• The ECF bit which when set causes an interrupt and the PCA overflow flag CF (in
the CCON SFR) to be set when the PCA timer overflows.
The CCON register contains the run control bit for the PCA and the flags for the PCA
timer (CF) and each module (Refer to Table 28).
• Bit CR (CCON.6) must be set by software to run the PCA. The PCA is shut off by
clearing this bit.
• Bit CF: The CF bit (CCON.7) is set when the PCA counter overflows and an
interrupt will be generated if the ECF bit in the CMOD register is set. The CF bit can
only be cleared by software.
76543210
CIDL WDTE - - - CPS1 CPS0 ECF
Bit
Number
Bit
Mnemonic Description
7CIDL
Counter Idle Control
Cleared to program the PCA Counter to continue functioning during idle Mode.
Set to program PCA to be gated off during idle.
6WDTE
Watchdog Timer Enable
Cleared to disable Watchdog Timer function on PCA Module 4.
Set to enable Watchdog Timer function on PCA Module 4.
5-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
3-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
2 CPS1 PCA Count Pulse Select
CPS1
CPS0Selected PCA input
0 0 Internal clock fCLK PERIPH/6
0 1 Internal clock fCLK PERIPH/2
1 0 Timer 0 Overflow
1 1 External clock at ECI/P1.2 pin (max rate = fCLK PERIPH/ 4)
1 CPS0
0ECF
PCA Enable Counter Overflow Interrupt
Cleared to disable CF bit in CCON to inhibit an interrupt.
Set to enable CF bit in CCON to generate an interrupt.