83C795 datasheet(21/136 Pages) SMSC

21 / 136 page

Mnemonic

Pin Number I/O

Description

R LE D

130

I/O

R E CV LE D DR IVE R . When on, R LE D drives low to turn on an

external LE D. If no data is received, R LE D is off. If data is

received, R LE D goes active for approximately 50ms longer than

the received packet length. T his pin als o s erves as the E E R OM

data in pin (E E DI) and is used as the s can data input (formerly

SCANIN) in s can mode.

R OMCS

138

BIOS R OM OUT PUT E NABLE . Active low. Chip S elect for R OM

BIOS . Us ed for XT XE in s ome test modes .

RX+

RX-

124

123

AUI R E CE IVE . T he Manches ter encoded data from the external

trans ceiver is received on R X+ / R X-.

S A19 - 14

S A13 - 11

S A10 - 09

S A08 - 06

S A05 - 00

88 - 83

78 - 76

44 - 43

38 - 37

35 - 30

I/O

PC ADDR E SS BUS. Normal timing vers ion of s ystem addres s

lines. T hes e s ignals are active high.

SBHE

PC BUS HIGH E NABLE . Active low. Indicates a trans fer of data on

the upper byte of the data bus, S D8 through S D15.

S D15 - 14

S D13 - 12

SD11 - 10

S D09 - 08

SD07

S D06 - 04

S D03 - 02

S D01 - 00

45 - 46

48 - 49

51 - 52

54 - 55

65 - 63

61 - 60

58 - 57

I/O

SYST E M DAT A BUS. Data input and output to hos t and shared

memory. T hes e signals are active high.

SME MR

I/O

LOW ME MORY RE AD S T ROBE . Reads buffer memory onto the

PC data bus . It is active only when the memory addres s is within

the first 1Mb of memory space. Active low.

SME MW

I/O

LOW ME MOR Y WR IT E S T R OBE . Writes buffer memory from the

PC data bus . S ME MW is active only when the memory address is

within the firs t 1Mb of memory s pace. Active low.

TE S T A

TE S T B

117

118

I/O-MAPPING CONTROL PINS. All signal pins on the 83C795

(except for the analog pins) have been divided into two groups,

GROUPA and GROUPB. The functionality of these pins is

controlled by the two test pins, as follows:

TESTA

TESTB

GROUPA

GROUPB

NORMAL

TRISTATE

TABLE 4-1. 83C795 PIN ASSIGNMENTS (CONT.)

83C795

PIN LIST

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