DP83905AVQB datasheet(6/80 Pages) NSC

6 / 80 page

20 Pin Description (Continued)

Pin No

Pin Name

Type

Description

NETWORK INTERFACE PINS (Continued)

X1 (OSCIN)

CRYSTAL OR EXTERNAL OSCILLATOR INPUT

XTAL

X2 (OSCOUT)

CRYSTAL FEEDBACK OUTPUT

Used in crystal connections only Should be left

completely unconnected when using an oscillator module

XTAL

THIN

THIN CABLE

This output is high if ATLANTIC Controller is configured for thin

cable It can be used to enable the DC-DC converter required by the thin ethernet

DCDC

configuration

EXTERNAL MEMORY SUPPORT

58–50

MSD0–7

IO I O

MEMORY SUPPORT DATA BUSCONFIGURATION REGISTER A INPUT

EEPROM SIGNALS

CA0–7

MOS

MSD0–7 When RESET is inactive these pins can be used to access external

DO DI SK

memory and boot PROM

CA0–7 When RESET is active Configuration Register A is loaded with the data

value on these pins If the user puts an external pull-up on any of these pins then the

corresponding register bit is set to a 1 If the pin is left unconnected then the register

bit is 0

DO DI SK When RESET goes from an active to an inactive level ATLANTIC

Controller will read the contents of an EEPROM using these signals and load the

contents into internal registers These internal registers will then be mapped into the

space taken up by the PROM in the NE2000 and Ethercard PLUS16 After the

EEPROM read operation has completed these pins will revert to MSD0–2 (D0 e

MSD0 DI e MSD1 SK e MSD2)

48–45

MSD8–15 or

IO I

MEMORY SUPPORT DATA BUSCONFIGURATION REGISTER B INPUT

43-40

CB0–7

MOS

MSD8–15 When RESET is inactive these pins can be used to access external

memory

CB0–7 When RESET is active Configuration Register B is loaded with the data

value on these pins If the user puts an external pull-up on any of these pins then the

corresponding register bit is set to a 1 If the pin is left unconnected then the register

bit is 0

31–25

MSA1–8 or

O I

MEMORY SUPPORT ADDRESS BUSCONFIGURATION REGISTER C INPUT

CC0–7

MOS

MSA1–8 When RESET is inactive these pins drive the memory support address

bus

CC0–7 When RESET is active Configuration Register C is loaded with the data

value on these pins If the user puts an external pull-up on any of these pins then the

corresponding register bit is set to a 1 If the pin is left unconnected then the register

bit is 0

21–15

MSA9–15

MEMORY SUPPORT ADDRESS BUS

MSA9–15 When RESET is inactive these

pins drive the memory support address bus When the memory is only 8 bits wide A0

MOS

will appear on A13 in compatible mode and on A15 in non-compatible mode

MSRD

MEMORY SUPPORT BUS READ

Strobes data from the external RAM into the AT

LANTIC Controller via the memory support data bus

MOS

MSWR

MEMORY SUPPORT BUS WRITE

Strobes data from the ATLANTIC Controller

into the external RAM via the memory support data bus

MOS

BPCS

BOOT PROM CHIP SELECT

Selects the boot PROM on the memory support data

bus

MOS

Driver Types are I e Input O e Output IO e Bi-directional Output OCH e Open Collector 3SH e TRI-STATE Output TTL e TTL Compatible AUI e

Attachment Unit Interface TPI e Twisted Pair Interface LED e LED Drive MOS e CMOS Level Compatible XTAL e Crystal

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