IBM EM78P312N manual 5.13 I/O Ports, Reset and Wake-up, Bit Microcontroller

EM78P312N

8-Bit Microcontroller

5.13 I/O Ports

The I/O registers, Port 6, Port 7, Port 8, and Port 9 are bi-directional tri-state I/O ports. Each I/O pin can be defined as “input” or “output” pin by the I/O control register (IOC6 ~ IOC9). The I/O registers and I/O control registers are both readable and writable. The I/O interface circuits for Port 6, Port 7, Port 8, and Port 9 are shown in Fig. 5-26.

		PCRD
	Q	P	D
		R
			CLK	PCW R
	Q	C
		L
PORT	Q	P		IOD
			D
		R
				PDW R
	Q	C CLK
		L
0	M			PDRD
1	U
	X

Fig. 5-27 The I/O Port and I/O Control Register Circuit

5.14 Reset and Wake-up

5.14.1 Reset

A reset is initiated by one of the following events:

(1)Power-on reset

(2)/RESET pin input “low”

(3)WDT timeout. (if enabled)

The device is kept in a reset condition for a period of approx. 18ms1 (one oscillator start-up timer period) after the reset is detected. Once a reset occurs, the following functions are performed.

„ The oscillator starts or is running

„ The Program Counter (R2) is reset to all “0”.

„ When power is switched on, the upper two bits of R3, the upper two bits of R4 and the Bits 6 ~ 4 of R5 are cleared.

„ All I/O port pins are configured as input mode (high-impedance state).

1 Note: VDD = 5V, set up time period = 16.2ms ± 30% VDD = 3V, set up time period = 19.6ms ± 30%

42 • Product Specification (V1.0) 10.03.2006

(This specification is subject to change without further notice)