COP888GD datasheet(13/42 Pages) NSC

13 / 42 page

Data Memory Segment RAM

Extension (Continued)

The 128 bytes of RAM contained in the base segment are

split between the lower and upper base segments. The first

112 bytes of RAM are resident from address 0000 to 006F in

the lower base segment, while the remaining 16 bytes of

RAM represent the 16 data memory registers located at ad-

dresses 00F0 to 00FF of the upper base segment. No RAM

is located at the upper sixteen addresses (0070 to 007F) of

the lower base segment.

Additional RAM beyond these initial 128 bytes, however, will

always be memory mapped in groups of 128 bytes (or less)

at the data segment address extensions (XX00 to XX7F) of

the lower base segment. The additional 128 bytes of RAM

are memory mapped at address locations 0100 to 017F hex.

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 tC 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.

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.

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 1 shows the variation in the oscillator frequencies as

functions of the component (R and C) values.

DS100076-6

*Reads as all ones.

FIGURE 5. RAM Organization

DS100076-7

RC > 5 x Power Supply Rise Time

FIGURE 6. Recommended Reset Circuit

COP888GD 数据表(PDF) 13 Page - National Semiconductor (TI)

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