COM20051 datasheet(8/82 Pages) SMSC

8 / 82 page

oscillator, pin 21 (XTAL1) functions as the clock

input.

Emulate Mode

The COM20051 contains a unique feature called

the

Emulate

mode

that

most

8051-based

peripheral

devices

not

accommodate.

TheEmulate mode permits developers to access

and program the internal ARCNET core using a

standard low-cost 8032 emulator.

This feature

eliminates the need for expensive dedicated

development equipment needed for other types

of 8051-based peripheral devices. The Emulate

mode is invoked by connecting the nEA pin to

VCC. This causes the internal 80C32 processor

to enter a HI-Z state and changes the state of the

COM20051 pins according to the following table:

Table 1 - Emulate Mode

SIGNAL NAME

EMUL = 0

EMUL = 1

PORT 0

Bidirectional

PORT 1

Bidirectional

HI-Z (except for pins

designated as interrupt

destinations)

PORT 2

Output

Input

INT0,1

(P3.2, P3.3)

Input

Output

RD/WR

(P3.6, P3.7)

Output

Input

ALE

Output

Input

TX,T0, T1

(P3.1,3.4,3.5)

nPSEN

Output

HI-Z

Address Decoding

The COM20051, as described previously, maps

the ARCNET registers into the 80C32's External

Data Memory space.

This provides system

flexibility because the location of the ARCNET

registers can be located anywhere within the 64K

External Data Memory space.

The precise

location can be resolved with a 256-byte page.

The location of that page in the External Data

Memory space is pointed to by the read/write

Address Decode Register, as shown in Figure 2.

The Address Decode Register is located at

FFFFh of the External Data Memory space. It

holds the upper 8 bits of the 16-bit address at

which the 256 page boundary will start.

This

to the ARCNET core.

The default value is

0000h.

The ARCNET core register page must be

mapped away from the external RAM prior to any

access to the external RAM by the software.

Failure to do this may result in incorrect data

write and read operations to the external RAM as

well as the core registers.

COM20051 Datasheet(PDF) 8 Page - SMSC Corporation

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