AT89C5131A-RDTIM datasheet(10/184 Pages) ATMEL

10 / 184 page

AT89C5130A/31A-M

4337C–USB–02/05

Table 11. System Signal Description

Signal

Name

Type

Description

Alternate

Function

AD[7:0]

I/O

Multiplexed Address/Data LSB for external access

Data LSB for Slave port access (used for 8-bit and 16-bit modes)

P0[7:0]

A[15:8]

I/O

Address Bus MSB for external access

Data MSB for Slave port access (used for 16-bit mode only)

P2[7:0]

I/O

Read Signal

Read signal asserted during external data memory read operation.

Control input for slave port read access cycles.

P3.7

I/O

Write Signal

Write signal asserted during external data memory write operation.

Control input for slave write access cycles.

P3.6

RST

Reset Input

Holding this pin low for 64 oscillator periods while the oscillator is running

resets the device. The Port pins are driven to their reset conditions when a

voltage lower than V

IL is applied, whether or not the oscillator is running.

This pin has an internal pull-up resistor which allows the device to be reset

by connecting a capacitor between this pin and VSS.

Asserting RST when the chip is in Idle mode or Power-down mode returns

the chip to normal operation.

This pin is tied to 0 for at least 12 oscillator periods when an internal reset

occurs ( hardware watchdog or power monitor).

ALE

Address Latch Enable Output

The falling edge of ALE strobes the address into external latch. This signal

is active only when reading or writing external memory using MOVX

instructions.

PSEN

Program

Test mode entry signal. This pin must be set to V

DD for normal operation.

External Access Enable

This pin must be held low to force the device to fetch code from external

program memory starting at address 0000h. It is latched during reset and

cannot be dynamically changed during operation.

Table 12. Power Signal Description

Signal

Name

Type

Description

Alternate

Function

AVSS

GND

Analog Ground

AVSS is used to supply the on-chip PLL and the USB PAD.

AVDD

PWR

Analog Supply Voltage

AVDD is used to supply the on-chip PLL and the USB PAD.

VSS

GND

Digital Ground

VSS is used to supply the buffer ring and the digital core.

UVSS

GND

USB Digital Ground

UVSS is used to supply the USB pads.

UCAP

PWR

USB Pad Power Capacitor

UCAP must be connect to an external capacitor for USB pad power supply

(for typical application see Figure 4 on page 12)

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