COP8-REF-AM datasheet(22/83 Pages) NSC

22 / 83 page

10.0 Functional Description

(Continued)

The crystal and other oscillator components should be

placed in close proximity to the CKI and CKO pins to mini-

mize printed circuit trace length.

The values for the external capacitors should be chosen to

obtain the manufacturer’s specified load capacitance for the

crystal when combined with the parasitic capacitance of the

trace, socket, and package (which can vary from 0 to 8 pF).

The guideline in choosing these capacitors is:

Manufacturer’s specified load cap = (C

1 *C2)/(C1 +C2)+

parasitic

2 can be trimmed to obtain the desired frequency. C2

should be less than or equal to C

Note: The low power design of the low speed oscillator

makes it extremely sensitive to board layout and load ca-

pacitance. The user should place the crystal and load ca-

pacitors within 1cm. of the device and must ensure that the

above equation for load capacitance is strictly followed. If

these conditions are not met, the application may have

problems with startup of the low speed oscillator.

TABLE 3. Startup Times

CKI Frequency

Startup Time

10 MHz

1–10 ms

3.33 MHz

3–10 ms

1 MHz

3–20 ms

455 kHz

10–30 ms

32 kHz (low speed oscillator)

2–5 sec

10.8.2 Clock Doubler

This device contains a frequency doubler that doubles the

frequency of the oscillator selected to operate the main

microcontroller core. The details of how to select either the

high speed oscillator or low speed oscillator are described in,

Power Saving Features. When the high speed oscillator

connected to CKI operates at 10 MHz, the internal clock

frequency is 20 MHz, resulting in an instruction cycle time of

0.5 µs. When the 32 kHz oscillator connected to L0 and L1 is

selected, the internal clock frequency is 64 kHz, resulting in

an instruction cycle of 152.6 µs. The output of the clock

doubler is called MCLK and is referenced in many places

within this document.

10.9 CONTROL REGISTERS

10.9.1 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

Start/Stop

control

timer

modes 1 and

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)

10.9.2 PSW Register (Address X'00EF)

T1PNDA

T1ENA

EXPND

BUSY

EXEN

GIE

Bit 7

Bit 0

The PSW register contains the following select bits:

Half Carry Flag

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

High Speed Oscillator

20006315

Low Speed Oscillator

20006316

FIGURE 11. Crystal Oscillator

COP8-REF-AM Datasheet(PDF) 22 Page - National Semiconductor (TI)

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