COP424C Datasheet, PDF (11/24 Pages) National Semiconductor (TI) – Single-Chip 1k and 2k CMOS Microcontrollers

Functional Description (Continued)
The HALT mode is the minimum power dissipation state
Note If the user has selected dual-clock with D0 as external
oscillator (option 30e2) AND the COP444C 424C is
running with the D0 clock the HALT mode either
hardware or software will NOT be entered Thus
the user should switch to the CKI clock to HALT Al-
ternatively the user may stop the D0 clock to mini-
mize power
CKO PIN OPTIONS
a Two-pin oscillator (Crystal) See Figure 9A
In a crystal controlled oscillator system CKO is used as
an output to the crystal network The HALT mode may be
entered by program control (HALT instruction) which
forces CKO high thus inhibiting the crystal network The
circuit can be awakened only by forcing the RESET pin to
a logic ‘‘0’’ (restart)
b One-pin oscillator (RC or external) See Figure 9B
If a one-pin oscillator system is chosen two options are
available for CKO
 CKO can be selected as the HALT I O port In that
case it is an I O flip-flop which is an indicator of the
HALT status An external signal can over-ride this pin
to start and stop the chip By forcing a high level to
CKO the chip will stop as soon as CKI is high and
CKO output will stay high to keep the chip stopped if
the external driver returns to high impedance state
By forcing a low level to CKO the chip will continue
and CKO will stay low
 As another option CKO can be a general purpose in-
put read into bit 2 of A (accumulator) upon execution
of an INIL instruction
OSCILLATOR OPTIONS
There are four basic clock oscillator configurations available
as shown by Figure 8
a Crystal Controlled Oscillator CKI and CKO are connect-
ed to an external crystal The instruction cycle time equals
the crystal frequency optionally divided by 4 8 or 16
b External Oscillator The external frequency is optionally
divided by 4 8 or 16 to give the instruction cycle time
CKO is the HALT I O port or a general purpose input
c RC Controlled Oscillator CKI is configured as a single pin
RC controlled Schmitt trigger oscillator The instruction
cycle equals the oscillation frequency divided by 4 CKO
is the HALT I O port or a general purpose input
d Dual oscillator By selecting the dual clock option pin D0
is now a single pin oscillator input Two configurations are
available RC controlled Schmitt trigger oscillator or exter-
nal oscillator
The user may software select between the D0 oscillator
(in that case the instruction cycle time equals the D0
oscillation frequency divided by 4) by setting the D0 latch
high or the CKI (CKO) oscillator by resetting D0 latch low
Note that even in dual clock mode the counter if mask-
programmed as a time-base counter is always connect-
ed to the CKI oscillator
For example the user may connect up to a 1 MHz RC
circuit to D0 for faster processing and a 32 kHz watch
crystal to CKI and CKO for minimum current drain and
time keeping
Note CTMA instruction is not allowed when chip is running
from D0 clock
Figures 10A and 10B show the clock and timer diagrams
with and without Dual clock
COP445C AND COP425C 24-PIN PACKAGE OPTION
If the COP444C 424C is bonded in a 24-pin package it be-
comes the COP445C 425C illustrated in Figure 2 Connec-
tion diagrams Note that the COP445C 425C does not con-
tain the four general purpose IN inputs (IN3 – IN0) Use of
this option precludes of course use of the IN options in-
terrupt feature external event counter feature and the
Microbus option which uses IN1 – IN3 All other options are
available for the COP445C 425C
Note If user selects the 24-pin package options 9 10 19
and 20 must be selected as a ‘‘0’’ (load to V_CC on the
IN inputs) See option list
COP426C 20-PIN PACKAGE OPTION
If the COP425C is bonded as 20-pin device it becomes the
COP426C Note that the COP426C contains all the
COP425C pins except D₀ D₁ G₀ and G₁
Block Diagram (Continued)
FIGURE 9A Halt Mode Two-Pin Oscillator
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TL DD 5259 – 10