93AA46A/B/C, 93LC46A/B/C, 93C46A/B/C
2.0
FUNCTIONAL DESCRIPTION
2.3
Data Protection
When the ORG pin (93XX46C) is connected to V
CC
,
the (x16) organization is selected. When it is connected
to ground, the (x8) organization is selected. Instruc-
tions, addresses and write data are clocked into the DI
pin on the rising edge of the clock (CLK). The DO pin is
normally held in a High-Z state except when reading
data from the device, or when checking the Ready/
Busy status during a programming operation. The
Ready/Busy status can be verified during an erase/
write operation by polling the DO pin; DO low indicates
that programming is still in progress, while DO high
indicates the device is ready. DO will enter the High-Z
state on the falling edge of CS.
All modes of operation are inhibited when V
CC
is below
a typical voltage of 1.5V for '93AA' and '93LC' devices
or 3.8V for '93C' devices.
The EWEN and EWDS commands give additional
protection against accidentally programming during
normal operation.
Note:
For added protection, an EWDS
command should be performed after
every write operation and an external 10
kΩ pull-down protection resistor should be
added to the CS pin.
2.1
Start Condition
The Start bit is detected by the device if CS and DI are
both high with respect to the positive edge of CLK for
the first time.
Before a Start condition is detected, CS, CLK and DI
may change in any combination (except to that of a
Start condition), without resulting in any device
operation (Read, Write, Erase, EWEN, EWDS, ERAL
or WRAL). As soon as CS is high, the device is no
longer in Standby mode.
An instruction following a Start condition will only be
executed if the required opcode, address and data bits
for any particular instruction are clocked in.
Note:
When preparing to transmit an instruction,
either the CLK or DI signal levels must be
at a logic low as CS is toggled active high.
After power-up, the device is automatically in the
EWDS mode. Therefore, an
EWEN
instruction must be
performed before the initial
ERASE
or
WRITE
instruction
can be executed.
Block Diagram
V
CC
V
SS
Address
Decoder
Memory
Array
Address
Counter
Data Register
DI
ORG*
CS
CLK
Mode
Decode
Logic
Clock
Register
Output
Buffer
DO
2.2
Data In/Data Out (DI/DO)
It is possible to connect the Data In and Data Out pins
together. However, with this configuration it is possible
for a “bus conflict” to occur during the “dummy zero”
that precedes the read operation, if A0 is a logic high
level. Under such a condition the voltage level seen at
Data Out is undefined and will depend upon the relative
impedances of Data Out and the signal source driving
A0. The higher the current sourcing capability of A0,
the higher the voltage at the Data Out pin. In order to
limit this current, a resistor should be connected
between DI and DO.
*ORG input is not available on A/B devices
DS21749F-page 6
©
2005 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
