XM20C64

2

PIN DESCRIPTIONS

The address inputs select an 8-bit memory location

during read and write operations.

Chip Enable (

CE)

The chip enable input must be LOW to enable all read,

write and user requested nonvolatile operations.

Output Enable (

OE)

During normal RAM operations

OE controls the data

output buffers. If a hardware nonvolatile operation is

selected (

NE = CE = LOW) and OE strobes LOW, a

recall operation will be initiated.

OE LOW will always disable a STORE operation regard-

less of the state of

NE, WE, and CE so long as the

internal transfer has not commenced.

Write Enable (

WE)

During normal RAM operations

WE = CE = LOW will

cause data to be written to the RAM address pointed to

Nonvolatile Enable (

NE)

The nonvolatile input controls the transfer of data from

LOW in conjunction with

CE = OE = LOW.

Data is written to or read from the X20C64 through the

I/O pins. The I/O pins are placed in the high impedance

state when either

CE or OE is HIGH or when NE is LOW.

AUTOSTORE Output (

AS)

AS is an open-drain output. When it is asserted (driving

threshold and an internal store operation has been

initiated. Because

AS is an open drain output it may be

wire-ORed with multiple open drain outputs and used as

an interrupt input to a microprocessor.

DEVICE OPERATION

NOVRAM operations are identical to those of a standard

SRAM. When

OE and CE are asserted data is presented

at the I/Os from the address location pointed to by the

RAM write operations are initiated and the address input

is latched by the HIGH to LOW transition of

CE or WE,

whichever occurs last. Data is latched on the rising edge

of either

CE or WE, whichever occurs first.

initiated whenever

OE = NE = CE = LOW. A recall is also

performed automatically upon power-up.

Command Sequence Operations

The X20C64 employs a version of the industry standard

Software Data Protection (SDP). The end user can

select various options for transferring data from RAM

All command sequences are comprised of three specific

data/address write operations performed with

NE LOW.

A Store operation can be directly selected by issuing a

Store command. The user may also enable and disable

the AUTOSTORE function through the software data

protection sequence. Refer to Table 1 below for a

complete description of the command sequence.

Operational Notes

The X20C64 should be viewed as a subsystem when

writing software for the various store operations. The

module contains four discrete components each need-

ing to be set to the required state individually. The two

the four components.