Timer Registers
M68HC12B Family Data Sheet, Rev. 9.1
Freescale Semiconductor
179
The two 8-bit pulse accumulators, PAC1 and PAC0, are cascaded to form the PACB 16-bit pulse
accumulator. When PACB in enabled, (PBEN = 1 in PBCTL, $B0) the PACN1 and PACN0 register
contents are, respectively, the high and low bytes of the PACB.
When PACN1 overflows from $FF to $00, the interrupt flag PBOVF in PBFLG ($B1) is set. Full count
register access should take place in one clock cycle. A separate read/write for high byte and low byte will
give a different result than accessing them as a word.
13.4.14 16-Bit Modulus Down-Counter Control Register
Read: Anytime
Write: Anytime
MCZI — Modulus Counter Underflow Interrupt Enable Bit
0 = Modulus counter interrupt is disabled.
1 = Modulus counter interrupt is enabled.
MODMC — Modulus Mode Enable Bit
0 = The counter counts once from the value written to it and will stop at $0000.
1 = Modulus mode is enabled. When the counter reaches $0000, the counter is loaded with the
latest value written to the modulus count register.
NOTE
For proper operation, the MCEN bit should be cleared before modifying the
MODMC bit to reset the modulus counter to $FF.
RDMCL
—
Read Modulus Down-Counter Load Bit
0 = Reads of the modulus count register will return the present value of the count register.
1 = Reads of the modulus count register will return the contents of the load register.
ICLAT
—
Input Capture Force Latch Action Bit
When input capture latch mode is enabled (LATQ and BUFEN bit in ICSYS ($AB) are set), writing 1 to
this bit immediately forces the contents of the input capture registers TC0 to TC3 and their
corresponding 8-bit pulse accumulators to be latched into the associated holding registers. The pulse
accumulators will be automatically cleared when the latch action occurs.
Writing 0 to this bit has no effect. Read of this bit aways will return 0.
FLMC — Force Load Register into the Modulus Counter Count Register Bit
This bit is active only when the modulus down-counter is enabled (MCEN = 1). Writing a 1 into this bit
loads the load register into the modulus counter count register. This also resets the modulus counter
prescaler. Writing 0 to this bit has no effect.
When MODMC = 0, the counter starts counting and stops at $0000. Reads of this bit will return
always 0.
Address: $00A6
Bit 7
6
5
4
3
2
1
Bit 0
Read:
MCZI
MODMC
RDMCL
ICLAT
FLMC
MCEN
MCPR1
MCPR0
Write:
Reset:
0
0
0
0
0
0
0
0
Figure 13-35. 16-Bit Modulus Down-Counter Control Register (MCCTL)