SL8X371
8-Bit Latched Bidirectional
I/O Port
Legacy Device:
Philips/Signetics S8X371
DESCRIPTION
The 8X371 I/O Port is a bidirectional device designed for use
as an interface element in systems that use TTL-compatible
busses. Typically, the 8X371 is used with the 8X305
Microcontroller and its associated interface Vector (IV) bus;
however, it can also be used with the 8X300 Microcontroller or
an equivalent microprocessor. The 8X371 is functionally the
same and pin-for pin compatible with the older 8T31/8X31 but
features improved performance and increased drive current. As
shown in the logic diagram of Figure 1, the 8X371 consists of
eight identical data latches — bits 0 through 7. The latches are
accessed from either of two 8-bit busses — the Microcontroller
(IV bus) and the user data (UD bus). Separate controls are pro-
vided for each bus and both busses operate independently, except
when both attempt to input data at the same time; in such situa-
tions, the user bus always has priority. A Master Enable (ME)
input over the IV bus. The data latches are transparent, in that,
while either bus is enabled for input, all input-data transitions are
propagated to the other bus, if enabled for output.
FEATURES
•
•
•
•
•
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Two bidirectional 8-bit busses
Independent bus operation (user-bus priority for data entry)
User data input synchronous with respect to MCLK
3-State TTL outputs with high-drive capabilities
Power-up to predetermined logic state
Directly compatible with 8X305 (or 8X300)
Microcontrollers
• Single +5V supply
• 0.4” 24-pin DIP
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