USER`S MANUAL

S3F80N8_UM_REV1.10

PORT3 (32-PIN S3F80N8)

Port 3 is a 4-bit I/O port with individually configurable pins. Port 3 pins are accessed directly by writing or reading the Port 3 data register, P3 at location E3H. P3.0-3.3 can serve as inputs and as outputs (push pull or opendrain).

Port 3 Control Registers (P3CON)

Port 3 has an 8-bit control registers: P3CON for P3.0-3.3. A reset clears the P3CON registers to “00H”, configuring all pins to input mode. You use control registers settings to select input or output mode (push-pull or open drain).

Port 3 Pull-up Resistor Control Register (P3PUR)

Using the port 3 pull-up resistor control register, P3PUR (F3H), you can configure pull-up resistors to individual port 3 pins.

MSB .7

.6

Port 3 Control Register (P3CON)

F2H, R/W

.5

.4

.3

.2

.1

.0

LSB

P3.1

P3.2

P3.3

P3CON bit-pair pin configuration settings:

0 0

0 1

1 0

1 1

Input mode

Output mode, push-pull

Output mode, open-drain

Not used

P3.0

Figure 9-12. Port 3 Control Register (P3CON)

9-11

I/O PORTS

MSB .7

Port 3 Pull-up Control Register (P3PUR)

F3H, R/W

.6

.5

.4

.3

.2

.1

.0

LSB

P3.3

P3.2

P3.1

P3.0

Not used

P3PUR bit configuration settings:

0

1

Disable pull-up resistor

Enable pull-up resistor

NOTE:

The reset value of P3PUR is pull-up enable.

Figure 9-13. Port 3 Pull-up Control Register (P3PUR)

S3F80N8_UM_REV1.10

9-12

S3F80N8_UM_REV1.10 BASIC TIMER and TIMER 0

10

BASIC TIMER and TIMER 0

OVERVIEW

The S3F80N8 has two default timers: an 8-bit basic timer and one 8-bit general-purpose timer/counter. The 8-bit timer/counter is called timer 0.

BASIC TIMER (BT)

You can use the basic timer (BT) in two different ways:

— As a watchdog timer to provide an automatic reset mechanism in the event of a system malfunction.

— To signal the end of the required oscillation stabilization interval after a reset or a stop mode release.

The functional components of the basic timer block are:

— Clock frequency divider (f osc

divided by 4096, 1024, 128) with multiplexer

— 8-bit basic timer counter, BTCNT (FDH, read-only)

— Basic timer control register, BTCON (D3H, read/write)

10-1