SAKC505CA-4EM 查看數據表（PDF） - Siemens AG

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SAKC505CA-4EM

8-Bit CMOS Microcontroller

Siemens AG 

C505 / C505C

C505A / C505CA

Table 3

Pin Definitions and Functions (cont’d)

Symbol

P2.0-P2.7

Pin Number I/O

*)

18-25

I/O

PSEN

26

O

ALE

27

O

*) I = Input

O = Output

Function

Port 2

is a an 8-bit quasi-bidirectional I/O port with internal pullup

resistors. Port 2 pins that have 1’s written to them are pulled

high by the internal pullup resistors, and in that state can be

used as inputs. As inputs, port 2 pins being externally pulled

low will source current (IIL, in the DC characteristics)

because of the internal pullup resistors. Port 2 emits the

high-order address byte during fetches from external

program memory and during accesses to external data

memory that use 16-bit addresses (MOVX @DPTR). In this

application it uses strong internal pullup transistors when

issuing 1s. During accesses to external data memory that

use 8-bit addresses (MOVX @Ri), port 2 issues the

contents of the P2 special function register and uses only

the internal pullup resistors.

The Program Store Enable

output is a control signal that enables the external program

memory to the bus during external fetch operations. It is

activated every three oscillator periods except during

external data memory accesses. Remains high during

internal program execution. This pin should not be driven

during reset operation.

The Address Latch Enable

output is used for latching the low-byte of the address into

external memory during normal operation. It is activated

every three oscillator periods except during an external data

memory access. When instructions are executed from

internal ROM or OTP (EA=1) the ALE generation can be

disabled by bit EALE in SFR SYSCON.

ALE should not be driven during reset operation.

Semiconductor Group

11

1997-12-01

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