PRINCIPLES OF OPERATION
The X68257 is a highly integrated peripheral device for
a wide variety of single-chip microcontrollers. The X68257
provides 32K-bytes of 5V E2PROM which can be used
either for program storage, data storage, or a combina-
tion of both, in systems based upon Von Neumann
(68XX) architectures. The X68257 incorporates the
interface circuitry normally needed to decode the control
signals and demultiplex the address/data bus to provide
a “seamless” interface.
The interface inputs on the X68257 are configured such
that it is possible to directly connect them to the proper
interface signals of the appropriate single-chip micro-
The X68257 features the industry standard 5V E2PROM
characteristics such as byte or page mode write and
Toggle Bit Polling.
44 PD2 MISO
45 PD3 MOSI
46 PD4 SCK
47 PD5 SS
Motorola 68XX operation requires the microcontroller
AS, E, and R/W outputs to be tied to the X68257 AS, E,
and R/W inputs respectively.
The falling edge of AS will latch the addresses for both
a read and write operation. The state of the R/W output
determines the operation to be performed, with the E
signal acting as a data strobe.
If R/W is HIGH and CE is HIGH (read operation) data will
be output on A/D0–A/D7 after E transitions HIGH. If
R/W is LOW and CE is HIGH (write operation) data
present at A/D0–A/D7 will be strobed into the X68257 on
the HIGH to LOW transition of E.
6539 ILL F03.2