
Block Diagram
standard CMOS SRAM nonvolatile during power-fail
conditions. During power-fail, the bq4285E/L auto-
matically write-protects the external SRAM and pro-
vides a VCC output sourced from the clock backup
battery.
Pin Descriptions
AD0–AD7
Multiplexed address/data input/
output
The bq4285E/L bus cycle consists of two
phases: the address phase and the data-
transfer phase. The address phase precedes
the data-transfer phase.
During the ad-
dress phase, an address placed on AD0–AD7
is latched into the bq4285E/L on the falling
edge of the AS signal.
During the data-
transfer phase of the bus cycle, the AD0–AD7
pins serve as a bidirectional data bus.
MOT
Connect to VSS for normal operation
The setting should not be changed during
system operation. MOT is internally pulled
low by a 20K
resistor. For the DIP and
SOIC packages, this pin is internally con-
nected to VSS, enabling the bus timing for
the Intel architecture.
CS
Chip select input
CS should be driven low and held stable
during the data-transfer phase of a bus cy-
cle accessing the bq4285E/L.
2
Bus
Type
MOT
Level
DS
Equivalent
R/W
Equivalent
AS
Equivalent
Intel
VSS
RD,
MEMR, or
I/OR
WR,
MEMW, or
I/OW
ALE
Table 1. Bus Setup
bq4285E/L