COP87L88FH Datasheet, PDF (15/45 Pages) National Semiconductor (TI) – 8-Bit CMOS OTP Microcontrollers with 16k Memory,

Timers (Continued)
Mode
TxC3
0
TxC2
1
1
1
3
0
1
1
1
TxC1
0
0
1
1
Description
Captures:
TxA Pos. Edge
TxB Pos. Edge
Captures:
TxA Pos. Edge
TxB Neg. Edge
Captures:
TxA Neg. Edge
TxB Neg. Edge
Captures:
TxA Neg. Edge
TxB Neg. Edge
Interrupt A
Source
Pos. TxA Edge
or Timer
Underflow
Pos. TxA
Edge or Timer
Underflow
Neg. TxA
Edge or Timer
Underflow
Neg. TxA
Edge or Timer
Underflow
Interrupt B
Source
Pos. TxB Edge
Neg. TxB
Edge
Neg. TxB
Edge
Neg. TxB
Edge
Timer
Counts On
t_C
t_C
t_C
t_C
Power Save Modes
The device offers the user two power save modes of opera-
tion: HALT and IDLE. In the HALT mode, all microcontroller
activities are stopped. In the IDLE mode, the on-board oscil-
lator circuitry and timer T0 are active but all other microcon-
troller activities are stopped. In either mode, all on-board
RAM, registers, I/O states, and timers (with the exception of
T0) are unaltered.
HALT MODE
The device can be placed in the HALT mode by writing a “1”
to the HALT flag (G7 data bit). All microcontroller activities,
including the clock and timers, are stopped. The WATCH-
DOG logic on the device is disabled during the HALT mode.
However, the clock monitor circuitry if enabled remains ac-
tive and will cause the WATCHDOG output pin (WDOUT) to
go low. If the HALT mode is used and the user does not want
to activate the WDOUT pin, the Clock Monitor should be dis-
abled after the device comes out of reset (resetting the Clock
Monitor control bit with the first write to the WDSVR register).
In the HALT mode, the power requirements of the device are
minimal and the applied voltage (V_CC) may be decreased to
V_r (V_r = 2.0V) without altering the state of the machine.
The device supports three different ways of exiting the HALT
mode. The first method of exiting the HALT mode is with the
Multi-Input Wakeup feature on the L port. The second
method is with a low to high transition on the CKO (G7) pin.
This method precludes the use of the crystal clock configura-
tion (since CKO becomes a dedicated output), and so may
be used with an RC clock configuration. The third method of
exiting the HALT mode is by pulling the RESET pin low.
Since a crystal or ceramic resonator may be selected as the
oscillator, the Wakeup signal is not allowed to start the chip
running immediately since crystal oscillators and ceramic
resonators have a delayed start up time to reach full ampli-
tude and frequency stability. The IDLE timer is used to gen-
erate a fixed delay to ensure that the oscillator has indeed
stabilized before allowing instruction execution. In this case,
upon detecting a valid Wakeup signal, only the oscillator cir-
cuitry is enabled. The IDLE timer is loaded with a value of
256 and is clocked with the t_c instruction cycle clock. The t_c
clock is derived by dividing the oscillator clock down by a fac-
tor of 10. The Schmitt trigger following the CKI inverter on
the chip ensures that the IDLE timer is clocked only when the
oscillator has a sufficiently large amplitude to meet the
Schmitt trigger specifications. This Schmitt trigger is not part
of the oscillator closed loop. The startup timeout from the
IDLE timer enables the clock signals to be routed to the rest
of the chip.
If an RC clock option is being used, the fixed delay is intro-
duced optionally. A control bit, CLKDLY, mapped as configu-
ration bit G7, controls whether the delay is to be introduced
or not. The delay is included if CLKDLY is set, and excluded
if CLKDLY is reset. The CLKDLY bit is cleared on reset.
The device has two mask options associated with the HALT
mode. The first mask option enables the HALT mode feature,
while the second mask option disables the HALT mode. With
the HALT mode enable mask option, the device will enter
and exit the HALT mode as described above. With the HALT
disable mask option, the device cannot be placed in the
HALT mode (writing a “1” to the HALT flag will have no effect,
the HALT flag will remain “0”).
IDLE MODE
The device is placed in the IDLE mode by writing a “1” to the
IDLE flag (G6 data bit). In this mode, all activities, except the
associated on-board oscillator circuitry, and the IDLE Timer
T0, are stopped.
The power supply requirements of the microcontroller in this
mode of operation are typically around 30% of normal power
requirement of the microcontroller.
As with the HALT mode, the device can be returned to nor-
mal operation with a reset, or with a Multi-Input Wakeup from
the L Port. Alternately, the microcontroller resumes normal
operation from the IDLE mode when the thirteenth bit (repre-
senting 4.096 ms at internal clock frequency of 1 MHz, t_c =
1 µs) of the IDLE Timer toggles.
This toggle condition of the thirteenth bit of the IDLE Timer
T0 is latched into the T0PND pending flag.
The user has the option of being interrupted with a transition
on the thirteenth bit of the IDLE Timer T0. The interrupt can
be enabled or disabled via the T0EN control bit. Setting the
T0EN flag enables the interrupt and vice versa.
The user can enter the IDLE mode with the Timer T0 inter-
rupt enabled. In this case, when the T0PND bit gets set, the
device will first execute the Timer T0 interrupt service routine
and then return to the instruction following the “Enter Idle
Mode” instruction.
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