56F803 datasheet(17/57 Pages) FREESCALE

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56F803 Technical Data, Rev. 16

Freescale Semiconductor

2.5 Interrupt and Program Control Signals

Table 2-7 Data Bus Signals

No. of

Pins

Signal

Name

Signal

Type

State During

Reset

Signal Description

D0–D15

Input/O

utput

Tri-stated

Data Bus— D0–D15 specify the data for external Program or Data

memory accesses. D0–D15 are tri-stated when the external bus is

inactive. Internal pull-ups may be active.

Table 2-8 Bus Control Signals

No. of

Pins

Signal

Name

Signal

Type

State During

Reset

Signal Description

Output

Tri-stated

Program Memory Select—PS is asserted low for external Program memory

access.

Output

Tri-stated

Data Memory Select—DS is asserted low for external Data memory access.

Output

Tri-stated

Write Enable—WR is asserted during external memory write cycles. When

WR is asserted low, pins D0–D15 become outputs and the device puts data

on the bus. When WR is deasserted high, the external data is latched inside

the external device. When WR is asserted, it qualifies the A0–A15, PS, and

DS pins. WR can be connected directly to the WE pin of a Static RAM.

Output

Tri-stated

Read Enable—RD is asserted during external memory read cycles. When

RD is asserted low, pins D0–D15 become inputs and an external device is

enabled onto the device data bus. When RD is deasserted high, the external

data is latched inside the controller. When RD is asserted, it qualifies the

A0–A15, PS, and DS pins. RD can be connected directly to the OE pin of a

Static RAM or ROM.

Table 2-9 Interrupt and Program Control Signals

No. of

Pins

Signal

Name

Signal

Type

State During

Reset

Signal Description

IRQA

Input

(Schmitt)

Input

External Interrupt Request A—The IRQA input is a synchronized

external interrupt request indicating an external device is requesting

service. It can be programmed to be level-sensitive or

negative-edge- triggered.

IRQB

Input

(Schmitt)

Input

External Interrupt Request B—The IRQB input is an external

interrupt request indicating an external device is requesting service.

It can be programmed to be level-sensitive or

negative-edge-triggered.

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