93C76/86
2.0
PRINCIPLES OF OPERATION
When the ORG pin is connected to V
CC
, the x16 orga-
nization is selected. When it is connected to ground, the
x8 organization is selected. Instructions, 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 dur-
ing a programming operation. The READY/BUSY sta-
tus 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. The DO will enter the high impedance state on
the falling edge of the CS.
low all programming operations. Execution of a READ
instruction is independent of both the EWEN and
EWDS instructions.
2.4
Data Protection
During power-up, all programming modes of operation
are inhibited until V
CC
has reached a level greater than
1.4V. During power-down, the source data protection
circuitry acts to inhibit all programming modes when
V
CC
has fallen below 1.4V.
The EWEN and EWDS commands give additional pro-
tection against accidentally programming during nor-
mal operation.
After power-up, the device is automatically in the
EWDS mode. Therefore, an EWEN instruction must be
performed before any ERASE or WRITE instruction can
be executed.
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 oper-
ation (READ, WRITE, ERASE, EWEN, EWDS, ERAL,
and WRAL). As soon as CS is HIGH, the device is no
longer in the standby mode.
An instruction following a START condition will only be
executed if the required amount of opcode, address
and data bits for any particular instruction are clocked
in.
After execution of an instruction (i.e., clock in or out of
the last required address or data bit) CLK and DI
become don't care bits until a new start condition is
detected.
2.2
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.
2.3
Erase/Write Enable and Disable
(EWEN, EWDS)
The 93C76/86 powers up in the Erase/Write Disable
(EWDS) state. All programming modes must be pre-
ceded by an Erase/Write Enable (EWEN) instruction.
Once the EWEN instruction is executed, programming
remains enabled until an EWDS instruction is executed
or V
CC
is removed from the device. To protect against
accidental data disturb, the EWDS instruction can be
used to disable all Erase/Write functions and should fol-
©
1996 Microchip Technology Inc.
Preliminary
DS21132C-page 5
MICROCHIP [ MICROCHIP TECHNOLOGY ]
