NEC Network Controller uPD98502 - Manual (Page 427)

Preliminary User’s Manual S15543EJ1V0UM 427
CHAPTER 10 MICRO WIRE
10.1 Overview
This EEPROM interface is compatible with the Micro Wire serial interface. Connection to the “NM93C46” serial
EEPROM, manufactured by National Semiconductor, is recommended.
Serial EEPROM memory area is accessed in-directly throghout Micro Wire-macro registers, that is ECCR and
ERDR registers. To access the EEPROM, the V
R
4120A writes a command into the ECCR register of Micro Wire-
macro. When Micro Wire-macro accepts the command, it executes the command via the EEPROM interface. To read
EEPROM data, the V R 4120A sets an address and READ command into the ECCR register. When the microwire-
macro is reading data, the MSB bit of the ERDR register is set to 1. Once the microwire-macro finishes reading the
data, it sets the MSB bit to 0 and stores the data in the EDAT field. After issuing the command, the V R 4120A checks
that the MSB bit of the ERDR register is set to 0, then obtains the data. To write data into or erase data from the
EEPROM, the V
R
4120A must enable write and erase operations using the EWEN command in advance. When no
EEPROM is connected, accessing these registers is meaningless.
This Micro Wire interface has also auto-load function. By this function, user can read 12-byte data of EEPROM (1H
to 6H of half-word unit) throughout MACAR1 to MACAR3 registers without ECCR register’s control. This auto-load
function works one-time after system boot. In addition, it is necessary for auto-loading to obey initial data format for
EEPROM (refer to under table).
During both auto-loading or loading by ECCR register, MSB bit of ERDR register is asserted to ‘1’ for flag of busy
state. At the end of EEPROM loading, MSB bit of ERDR register is de-asserted to ‘0’, and then USER can read
MACAR1 to MACAR3 registers or [15:0] field of ERDR register.