Signal Name

Signal

State During

Signal Description

Type

Reset

SXFC

Input

Input

External Filter Capacitor— This pin is used to add an external fil-

ter circuit to the PLL.

2.3

External Memory Interface (Port A)

Table 2-5. Address Bus Signals

Signal

State

Signal Name

During

Signal Description

Type

Reset

A0–A15

Output

Tri-stated

Address Bus— Signals A0–A15 change in T0 and specify the

address for an external program or data memory access. The value

of the DRV bit in the bus control register (BCR) causes the address

bus to retain the last external address (DRV = 1) or to be tri-stated

(DRV = 0) during an internal access or in stop or wait mode. See

Section 4.2.1, “Bus Control Register (BCR),” on page 4-3.

Table 2-6. Data Bus Signals

Signal

State

Signal Name

During

Signal Description

Type

Reset

D0–D15

Input/

Tri-stated

Data Bus— Read data is sampled in on the trailing edge of T2, while

output

write data output is enabled on the leading edge of T2 and tri-stated

on the leading edge of T0. D0–D15 are tri-stated when the external

bus is inactive.

Table 2-7. Bus Control Signals

Signal

State

Signal Name

During

Signal Description

Type

Reset

Output

Pulled

Program Memory Select—

is asserted low for external program

PS

PS

high

memory access. If the external bus is not used during an instruction

internally

cycle (T0, T1, T2, or T3),

PS

is deasserted high in T0. During an

internal access in stop or wait mode, the value of the DRV bit in the

BCR determines whether the chip continues to drive

PS

(DRV = 1)

or tri-states

PS

(DRV = 0).

Output

Pulled

Data Memory Select—

is asserted low during T0 for external

DS

DS

high

data memory access. If the external bus is not accessed during an

internally

instruction cycle (T0, T1, T2, or T3),

DS

is deasserted high in T0.

During an internal access in stop or wait mode, the value of the

DRV bit in the BCR determines whether the chip continues to drive

DS

(DRV = 1) or tri-states

DS

(DRV = 0).

2-4

DSP56824 User’s Manual