COP224C Datasheet, PDF (9/24 Pages) National Semiconductor (TI) – Single-Chip 1k and 2k CMOS Microcontrollers

Functional Description (Continued)
HALT MODE
The COP244C 245C 224C 225C 226C is a FULLY STAT-
IC circuit therefore the user may stop the system oscillator
at any time to halt the chip The chip may also be halted by
the HALT instruction or by forcing CKO high when it is
mask-programmed as a HALT I O port Once in the HALT
mode the internal circuitry does not receive any clock sig-
nal and is therefore frozen in the exact state it was in when
halted All information is retained until continuing The chip
may be awakened by one of two different methods
 Continue function by forcing CKO low if it mask-pro-
grammed as a HALT I O port the system clock is re-en-
abled and the circuit continues to operate from the point
where it was stopped
 Restart by forcing the RESET pin low (see Initializa-
tion)
The HALT mode is the minimum power dissipation state
CKO PIN OPTIONS
a Two-pin oscillator (Crystal) See Figure 6a
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 6b
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
Block Diagram
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 three basic clock oscillator configurations avail-
able as shown by Figure 5
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
Figure 7 shows the clock and timer diagram
COP245C AND COP225C 24-PIN PACKAGE OPTION
If the COP244C 224C is bonded in a 24-pin package it be-
comes the COP245C 225C illustrated in Figure 2 Connec-
tion diagrams Note that the COP245C 225C does not con-
tain the four general purpose IN inputs (IN3 – IN0) Use of
this option precludes of course use of the IN options inter-
rupt feature external event counter feature
Note If user selects the 24-pin package options 9 10 19 and 20 must be
selected as a ‘‘2’’ See option list
COP226C 20-PIN PACKAGE OPTION
If the COP225C is bonded as 20-pin device it becomes the
COP226C Note that the COP226C contains all the
COP225C pins except D₀ D₁ G₀ and G₁
FIGURE 6a Halt Mode Two-Pin Oscillator
TL DD 8422 – 8
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