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8XC196Kx,8XC196Jx,87C196CA microcontroller family user's manual.1995.pdf
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8XC196Kx, Jx, CA USER’S MANUAL

 

 

 

VCC

 

 

 

 

 

 

4..7 kΩ††

 

 

 

 

 

 

 

Extternall

XTAL1

Cllock IInputt

 

 

 

 

 

 

 

 

 

 

 

 

Cllock Driverr

8XC196Device

 

 

 

 

No Connection

 

XTAL2

 

 

 

 

 

 

 

 

 

†† Requiired if TTL driverr is used.. Nott needed if CMOS driverr isused..

A0274-02-

Figure 13-5. External Clock Connections

TXHXX

TXLXH

TXHXL

0.7 VCC + 0.5 V

T

0.7 VCC + 0.5 V

 

 

 

XLXX

 

 

0.3 VCC – 0.5 V

0.3 VCC – 0.5 V

 

 

T

 

 

XLXL

 

 

A2119-02

Figure 13-6. External Clock Drive Waveforms

At power-on, the interaction between the internal amplifier and its feedback capacitance (i.e., the Miller effect) may cause a load of up to 100 pF at the XTAL1 pin if the signal at XTAL1 is weak (such as might be the case during start-up of the external oscillator). This situation will go away when the XTAL1 input signal meets the VIL and VIH specifications (listed in the datasheet). If these specifications are met, the XTAL1 pin capacitance will not exceed 20 pF.

13.5 RESETTING THE DEVICE

Reset forces the device into a known state. As soon as RESET# is asserted, the I/O pins, the control pins, and the registers are driven to their reset states. (Tables in Appendix B list the reset states of the pins (see Table B-8 on page B-20 for the 8XC196Kx, Table B-9 on page B-21 for the 8XC196Jx, or Table B-10 on page B-22 for the 87C196CA). See Table C-2 on page C-2 for the reset values of the SFRs.) The device remains in its reset state until RESET# is deasserted. When RESET# is deasserted, the bus controller fetches the chip configuration bytes (CCBs), loads them into the chip configuration registers (CCRs), and then fetches the first instruction.

13-8

MINIMUM HARDWARE CONSIDERATIONS

Figure 13-7 shows the reset-sequence timing. Depending upon when RESET# is brought high, the CLKOUT signal may become out of phase with the PH1 internal clock. When this occurs, the clock generator immediately resynchronizes CLKOUT as shown in Case 2.

Internal

Reset

RESET#

Pin

Case 1

CLKOUT

Case 2

CLKOUT

ALE

RD#

AD7:0

AD15:8

Phases Resynchronized

 

 

= ADV# Selected

 

9 TOSC

7 TOSC

9 TOSC

8 TOSC

 

7 TOSC

9 T

OSC

7 TOSC

11 T

OSC

18H

CCB0

 

1AH

CCB1

 

80H

20H

Weak

 

20H

Weak

 

20H

Bus parameters defined by CCB0 (ready control, bus width, and bus-timing modes) take effect here.

Defaultstotoanan8-bit8-bitbusbuntils untilthe CCBsthe CCBsare loadredloaded. AD15:8. AD15:8weakly drivestronglyaddressdriveduringaddressthe CCBduringfetchesthe. CCB fetchesFor 16-bit. Forsystems,16-bitwritesystems,20H to writethe high20HbytetooftheCCB0highandbyteCCB1of CCB0(2019HandCCB1201BH)(2019Hin orderandto prevent201BH) in orderbus contentionto prevent. bus contention.

A3084-01

Figure 13-7. Reset Timing Sequence

The following events will reset the device (see Figure 13-8):

an external device pulls the RESET# pin low

the CPU issues the reset (RST) instruction

the CPU issues an idle/powerdown (IDLPD) instruction with an illegal key operand

the watchdog timer (WDT) overflows

the oscillator fail detect (OFD) circuitry is enabled and an oscillator failure occurs

The following paragraphs describe each of these reset methods in more detail.

13-9

8XC196Kx, Jx, CA USER’S MANUAL

 

 

Internal

External

 

Reset State

VCC

 

 

Clock

 

Internal

Machine

RRST

 

Reset

Trigger

 

 

 

Signal

 

 

 

 

 

 

Count Complete

 

 

 

 

~200 Ω

RESET#

 

CLR

 

 

 

 

 

Q

Q1

 

 

 

 

 

SET

 

 

RST Instruction

 

 

 

WDT Overflow

 

 

 

IDLPD Invalid Key

 

 

 

USFR.0

OFD

(FOSC < 100 kHz)

See the datasheet for minimum and maximum RRST values.

A0034-02

Figure 13-8. Internal Reset Circuitry

13.5.1 Generating an External Reset

To reset the device, hold the RESET# pin low for at least one state time after the power supply is within tolerance and the oscillator has stabilized. When RESET# is first asserted, the device turns on a pull-down transistor (Q1) for 16 state times. This enables the RESET# signal to function as the system reset.

The simplest way to reset the device is to insert a capacitor between the RESET# pin and VSS, as

shown in Figure 13-9. The device has an internal pull-up (RRST) (Figure 13-8). RESET# should remain asserted for at least one state time after VCC and XTAL1 have stabilized and met the op-

erating conditions specified in the datasheet. A capacitor of 4.7 µF or greater should provide sufficient reset time, as long as VCC rises quickly.

13-10

MINIMUM HARDWARE CONSIDERATIONS

RESET#

+

4.7 μF

8XC196 Device

A0276--01

Figure 13-9. Minimum Reset Circuit

The other devices may not be reset because the capacitor will keep the voltage above VIL. Since RESET# is asserted for only 16 state times, it may be necessary to lengthen and buffer the systemreset pulse. Figure 13-10 shows an example of a system-reset circuit. In this example, D2 creates a wired-OR gate connection to the reset pin. An internal reset, system power-up, or SW1 closing will generate the system-reset signal.

 

VCC

 

(1)

 

VCC

 

(2)

D1

R

D2

 

 

4.7 kΩ

 

 

RESET#

SW1

C

Schmitt Triggers

 

 

 

 

 

8XC196

 

 

Device

 

 

System reset signal

 

 

to external circuitry

Notes:

1.D1 provides a faster cycle time for repetitive power-on resets.

2.Optional pull-up for faster recovery.

A0277-02

Figure 13-10. Example System Reset Circuit

13-11

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