intersil 82C55A Technical Brief

Introduction

TM

Technical Brief October 1997 TB357

82C55A Address to Read/Write Set Up Time

Author: Gene Faherty

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This Tech Brief applies only to the 51864 mask 82C55A
CMOS Programmable Peripheral Interface Circuit.

The Read/Write Logi c implementation of the 51864 mask (L7
version) of the 82C55A, while functionally equivalent to pre­vious mask versions, is slightly different. The “Address Sta­ble Before READ”, tAR, and “Address Stable Before
WRITE”, tAW, timing requirements remain specified at 0ns
minimum, but on the newer 51864 mask version, a falling
edge on the READ or WRITE signal disables further
changes on the Address Lines (A0 and A1) during the READ
or WRITE operation. This prevents the user from holding the
READ or WRITE line asserted low and changing the
Address Lines (A0 and A1) to access dif ferent ports or regis­ters on the 82C55A. This “disabling of address line change”
during READ or WRITE, would not occur on previous mask
versions of the 82C55A.

IMPACT - The “disabling of address line change” on the
falling edge of READ or WRITE should not affect any
application sinc e the RE AD or WR ITE sign al gener ated by
the driving device (µP) will always be una sserted prior to
changing the address and then be reasserted (READ or
WRITE) after the new address has been established.
However, some incoming tests may catch this difference
and indicate a failure.

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Technical Brief 357

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