COPCH942C Datasheet, PDF (13/26 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based Microcontrollers with 1k or 2k

Functional Description (Continued)
The program memory is addressed by the 15-bit program
counter (PC). ROM can be indirectly read by the LAID in-
struction for table lookup.
DATA MEMORY
The data memory address space includes on chip RAM, I/O
and registers. Data memory is addressed directly by the in-
struction or indirectly by the B, X and SP registers.
The COP820C family has 64 bytes of RAM and the
COP840C family has 128 bytes of RAM. Sixteen bytes of
RAM are mapped as “registers” that can be loaded immedi-
ately, decremented or tested. Three specific registers: B, X
and SP are mapped into this space, the other bytes are
available for general usage.
The instruction set permits any bit in memory to be set, reset
or tested. All I/O and registers (except the A & PC) are
memory mapped; therefore, I/O bits and register bits can be
directly and individually set, reset and tested.
Note: RAM contents are undefined upon power-up.
RESET
The RESET input when pulled low initializes the microcon-
troller. Initialization will occur whenever the RESET input is
pulled low. Upon initialization, the ports L and G are placed in
the TRI-STATE mode and the Port D is set high. The PC,
PSW and CNTRL registers are cleared. The data and con-
figuration registers for Ports L & G are cleared.
The external RC network shown in Figure 3 should be used
to ensure that the RESET pin is held low until the power sup-
ply to the chip stabilizes.
OSCILLATOR CIRCUITS
Figure 4 shows the three clock oscillator configurations.
A. CRYSTAL OSCILLATOR
The device can be driven by a crystal clock. The crystal net-
work is connected between the pins CKI and CKO.
Table 1 shows the component values required for various
standard crystal values.
B. EXTERNAL OSCILLATOR
CKI can be driven by an external clock signal. CKO is avail-
able as a general purpose input and/or HALT restart control.
C. R/C OSCILLATOR
CKI is configured as a single pin RC controlled Schmitt trig-
ger oscillator. CKO is available as a general purpose input
and/or HALT restart control.
Table 2I shows the variation in the oscillator frequencies as
functions of the component (R and C) values.
DS009103-10
FIGURE 4. Crystal and R-C Connection Diagrams
DS009103-9
RC ≥ 5X Power Supply Rise Time
FIGURE 3. Recommended Reset Circuit
OSCILLATOR MASK OPTIONS
The device can be driven by clock inputs between DC and
10 MHz.
R1
(kΩ)
0
0
0
R2
(MΩ)
1
1
1
TABLE 1. Crystal Oscillator Configuration, T_A = 25˚C
C1
C2
CKI Freq
(pF)
(pF)
(MHz)
30
30–36
10
30
30–36
4
200
100–150
0.455
Conditions
V_CC = 5V
V_CC = 5V
V_CC = 5V
TABLE 2. RC Oscillator Configuration, T_A = 25˚C
R
C
(kΩ)
(pF)
3.3
82
5.6
100
6.8
100
Note 19: 3k ≤ R ≤ 200k, 50 pF ≤ C ≤ 200 pF
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
13
Conditions
V_CC = 5V
V_CC = 5V
V_CC = 5V
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