Philips Semiconductors

Product specification

87C652/87C654

80C51 8-bit microcontroller

1999 Jul 23

7

OSCILLATOR

CHARACTERISTICS

XTAL1 and XTAL2 are the input and output,

respectively, of an inverting amplifier. The

pins can be configured for use as an on-chip

oscillator, as shown in the Logic Symbol.

To drive the device from an external clock

source, XTAL1 should be driven while XTAL2

is left unconnected. There are no

requirements on the duty cycle of the

external clock signal, because the input to

the internal clock circuitry is through a

divide-by-two flip-flop. However, minimum

and maximum high and low times specified in

the data sheet must be observed.

Reset

A reset is accomplished by holding the RST

pin high for at least two machine cycles (24

oscillator periods), while the oscillator is

running. To insure a good power-on reset, the

RST pin must be high long enough to allow

the oscillator time to start up (normally a few

milliseconds) plus two machine cycles. At

come up at the same time for a proper

start-up.

Idle Mode

In the idle mode, the CPU puts itself to sleep

while all of the on-chip peripherals stay

active. The instruction to invoke the idle

mode is the last instruction executed in the

normal operating mode before the idle mode

is activated. The CPU contents, the on-chip

RAM, and all of the special function registers

remain intact during this mode. The idle

mode can be terminated either by any

enabled interrupt (at which time the process

is picked up at the interrupt service routine

and continued), or by a hardware reset which

starts the processor in the same manner as a

power-on reset.

Power-Down Mode

In the power-down mode, the oscillator is

stopped and the instruction to invoke

power-down is the last instruction executed.

Only the contents of the on-chip RAM are

preserved. A hardware reset is the only way

to terminate the power-down mode. The

control bits for the reduced power modes are

in the special function register PCON. Table 2

shows the state of the I/O ports during low

current operating modes.

COMMUNICATION—SIO1

serial port on the 8XC552. The operation of

this subsystem is described in detail in the

8XC552 section of this manual.

Note that in both the 8XC652/4 and the

to port pins P1.6 and P1.7. Because of this,

P1.6 and P1.7 on these parts do not have a

pull-up structure as found on the 80C51.

Therefore P1.6 and P1.7 have open drain

outputs on the 8XC652/4.

Table 2. External Pin Status During Idle and Power-Down Mode

MODE

PROGRAM

MEMORY

ALE

PSEN

PORT 0

PORT 1

PORT 2

PORT 3

Idle

Internal

1

1

Data

Data

Data

Data

Idle

External

1

1

Float

Data

Address

Data

Power-down

Internal

0

0

Data

Data

Data

Data

Power-down

External

0

0

Float

Data

Data

Data

Serial Control Register (S1CON) – See Table 3

S1CON (D8H)

CR2

ENS1

STA

STO

SI

AA

CR1

CR0

Bits CR0, CR1 and CR2 determine the serial clock frequency that is generated in the master mode of operation.

Table 3. Serial Clock Rates

CR2

CR1

CR0

6 MHZ

12 MHz

16 MHz

20 MHz

0

0

0

23

47

62.5

78

256

0

0

1

27

54

71

224

0

1

0

31.25

62.5

83.3

192

0

1

1

37

75

100

160

1

0

0

6.25

12.5

17

21

960

1

0

1

50

100

120

1

1

0

100

60

1

1

1

0.25 < 62.5

0 to 255

0.5 < 62.5

0 to 254

0.65 < 55.6

0 to 253

0.81 < 69.4

0 to 253

96

× (256 – (reload value Timer 1))

(Reload value range: 0 – 254 in mode 2)

NOTE: