II CORE BLOCK: INITIAL RESET

II-3 INITIAL RESET

Pins for Initial Reset

Table 3.1 shows the pins used for initial reset.

 

 

Table 3.1 Pins for Initial Reset

Pin name

I/O

Function

#RESET

I

Initial reset input pin (Low active)

 

 

Low: Resets the CPU.

#MNI

I

NMI request input pin

 

 

This pin is also used for selecting a reset method.

 

 

High: Cold start

 

 

Low: Hot start

The chip is reset when the #RESET pin goes low and starts operating at the rising edge of the reset signal. The CPU and internal peripheral circuits are initialized while the #RESET pin is low.

Cold Start and Hot Start

The CPU supports two initial reset methods: cold start and hot start. The #MNI pin is used with the #RESET pin to set this condition.

The differences between cold start and hot start are shown in Table 3.2.

Table 3.2 Differences between Cold Start and Hot Start

Setup contents

Cold start

Hot start

Reset condition

#RESET = low & #MNI = high

#RESET = low & #MNI = low

CPU: PC

The vector at the boot address is loaded to the PC.

CPU: PSR

All the PSR bits are reset to 0.

CPU: Other registers

Undefined

CPU: Operating clock

The CPU operates with the OSC3 clock.

External bus status (0x48120–0x4813F)

Initialized

Status is retained.

Oscillation circuit

Both the OSC1 and OSC3 circuits start oscillating.

I/O pin status (0x402C0–0x402DF)

Initialized

Status is retained.

Other peripheral circuit

Initialized or undefined

Since cold start initializes all the internal peripheral circuits as well as the CPU, it is useful as a power-on reset. Hot start initializes the CPU and peripheral circuits, but does not reset the bus control unit and the input, output and I/O port status. It is therefore useful as a reset that maintains the external bus and I/O pin status during operation.

The #NMI pin that specifies the reset method should be set following the timing chart shown in Figure 3.1.

Cold start is generated

Hot start is generated

(#RESET = low & #NMI = high)

(#RESET = low & #NMI = low)

#NMI

#NMI

#RESET

#RESET

#NMI must be set to high longer than

#NMI must be set to low longer than

the reset pulse width.

the reset pulse width.

(1) Cold start

(2) Hot start

Figure 3.1 Setup of #RESET and #NMI Pins

S1C33210 FUNCTION PART

EPSON

B-II-3-1