COP888EK Datasheet, PDF (16/46 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based Microcontrollers with 8k Memory, Comparator, and Single-slope A/D Capability

Reset
The RESET input when pulled low initializes the microcon-
troller. Initialization will occur whenever the RESET input is
pulled low. Upon initialization, the data and configuration
registers for ports L, G and C are cleared, resulting in these
Ports being initialized to the TRI-STATE mode. Pin G1 of the
G Port is an exception (as noted below) since pin G1 is dedi-
cated as the WATCHDOG and/or Clock Monitor error output
pin. Port D is set high. The PC, PSW, ICNTRL, CNTRL,
T2CNTRL and T3CNTRL control registers are cleared. The
Comparator Select Register is cleared. The S register is ini-
tialized to zero. The Multi-Input Wakeup registers WKEN and
WKEDG are cleared. Wakeup register WKPND is unknown.
The stack pointer, SP, is initialized to 6F hex.
The device comes out of reset with both the WATCHDOG
logic and the Clock Monitor detector armed, with the
WATCHDOG service window bits set and the Clock Monitor
bit set. The WATCHDOG and Clock Monitor circuits are in-
hibited during reset. The WATCHDOG service window bits
being initialized high default to the maximum WATCHDOG
service window of 64k t_C clock cycles. The Clock Monitor bit
being initialized high will cause a Clock Monitor error follow-
ing reset if the clock has not reached the minimum specified
frequency at the termination of reset. A Clock Monitor error
will cause an active low error output on pin G1. This error
output will continue until 16 t_C–32 t_C clock cycles following
the clock frequency reaching the minimum specified value,
at which time the G1 output will enter the TRI-STATE mode.
The external RC network shown in Figure 6 should be used
to ensure that the RESET pin is held low until the power sup-
ply to the chip stabilizes.
R/C OSCILLATOR
By selecting CKI as a single pin oscillator input, a single pin
R/C oscillator circuit can be connected to it. CKO is available
as a general purpose input, and/or HALT restart input.
Note: Use of the R/C oscillator option will result in higher electromagnetic
emissions.
Table 2 shows the variation in the oscillator frequencies as
functions of the component (R and C) values.
DS012094-8
DS012094-9
FIGURE 7. Crystal and R/C Oscillator Diagrams
TABLE 1. Crystal Oscillator Configuration, T_A = 25˚C
R1
(kΩ)
0
0
0
R2
(MΩ)
1
1
1
C1
C2
(pF) (pF)
30 30–36
30 30–36
200 100–150
CKI Freq
(MHz)
10
4
0.455
Conditions
V_CC = 5V
V_CC = 5V
V_CC = 5V
RC > 5 x Power Supply Rise Time
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FIGURE 6. Recommended Reset Circuit
Oscillator Circuits
The chip can be driven by a clock input on the CKI input pin
which can be between DC and 10 MHz. The CKO output
clock is on pin G7 (crystal configuration). The CKI input fre-
quency is divided down by 10 to produce the instruction
cycle clock (1/t_c).
Note: External clocks with frequencies above about 4 MHz require the user
to drive the CKO (G7) pin with a signal 180 degrees out of phase with
CKI.
Figure 7 shows the Crystal and R/C oscillator diagrams.
CRYSTAL OSCILLATOR
CKI and CKO can be connected to make a closed loop crys-
tal (or resonator) controlled oscillator.
Table 1 shows the component values required for various
standard crystal values.
TABLE 2. RC Oscillator Configuration, T_A = 25˚C
R
C
(kΩ) (pF)
3.3 82
5.6 100
6.8 100
CKI Freq
(MHz)
2.2 to 2.7
1.1 to 1.3
0.9 to 1.1
Instr. Cycle
(µs)
3.7 to 4.6
7.4 to 9.0
8.8 to 10.8
Conditions
V_CC = 5V
V_CC = 5V
V_CC = 5V
Note 27: 3k ≤ R ≤ 200k
50 pF ≤ C ≤ 200 pF
Control Registers
CNTRL Register (Address X'00EE)
T1C3 T1C2 T1C1 T1C0 MSEL IEDG SL1 SL0
Bit 7
Bit 0
The Timer1 (T1) and MICROWIRE/PLUS control register
contains the following bits:
T1C3
Timer T1 mode control bit
T1C2
Timer T1 mode control bit
T1C1
Timer T1 mode control bit
T1C0
Timer T1 Start/Stop control in timer
modes 1 and 2, T1 Underflow Interrupt
Pending Flag in timer mode 3
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