COP888XG Datasheet, PDF (18/53 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based Microcontrollers with 4k to 24k Memory, Comparators and USART

Reset (Continued)
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).
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.
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.
Table 2 shows the variation in the oscillator frequencies as
functions of the component (R and C) values.
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FIGURE 7. Crystal and R/C Oscillator Diagrams
TABLE 1. Crystal Oscillator Configuration, T_A = 25˚C
R1 R2 C1
C2 CKI Freq Conditions
(kΩ) (MΩ) (pF) (pF)
(MHz)
0
1 30 30–36
10
V_CC = 5V
R1
(kΩ)
0
0
R2
(MΩ)
1
1
C1
C2
(pF) (pF)
30 30–36
200 100–150
CKI Freq
(MHz)
4
0.455
Conditions
V_CC = 5V
V_CC = 2.5V
TABLE 2. RC Oscillator Configuration, T_A = 25˚C
R
C CKI Freq Instr. Cycle Conditions
(kΩ) (pF)
(MHz)
3.3 82 2.2 to 2.7
5.6 100 1.1 to 1.3
6.8 100 0.9 to 1.1
Note: 3k ≤ R ≤ 200k
50 pF ≤ C ≤ 200 pF
(µs)
3.7 to 4.6
7.4 to 9.0
8.8 to 10.8
V_CC = 5V
V_CC = 5V
V_CC = 5V
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
MSEL
Selects G5 and G4 as MICROWIRE/PLUS
signals SK and SO respectively
IEDG
External interrupt edge polarity select
(0 = Rising edge, 1 = Falling edge)
SL1 & SL0 Select the MICROWIRE/PLUS clock divide
by (00 = 2, 01 = 4, 1x = 8)
PSW Register (Address X'00EF)
HC C T1PNDA T1ENA EXPND BUSY EXEN GIE
Bit 7
Bit 0
The PSW register contains the following select bits:
HC
Half Carry Flag
C
Carry Flag
T1PNDA Timer T1 Interrupt Pending Flag (Autoreload
RA in mode 1, T1 Underflow in Mode 2, T1A
capture edge in mode 3)
T1ENA Timer T1 Interrupt Enable for Timer Underflow
or T1A Input capture edge
EXPND External interrupt pending
BUSY MICROWIRE/PLUS busy shifting flag
EXEN Enable external interrupt
GIE
Global interrupt enable (enables interrupts)
The Half-Carry flag is also affected by all the instructions that
affect the Carry flag. The SC (Set Carry) and R/C (Reset
Carry) instructions will respectively set or clear both the carry
flags. In addition to the SC and R/C instructions, ADC,
SUBC, RRC and RLC instructions affect the Carry and Half
Carry flags.
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