• False Start Bit Detection.
• Complete Status Reporting Capabilities.
• Line Break Generation and Detection.
• Internal Diagnostic Capabilities.
Loopback Controls for Communications Link Fault
Isolation.
Break, Parity, Overrun, Framing Error Simulation.
• Full Prioritized Interrupt System Controls.
All communications protocol
is
a function
of
the system microcode
and must be loaded before the adapter
is
operational. All pacing ofthe
interface and control signal status must be handled by the system
software.
Asynchronous Communications Block Diagram
ADDRESS
BUSS
CHIP
SELECT
ADDRESS
DECODE
DATA
BUS
INTERRUPT
8250
ASYNCH
RONOUS
COMMUNICATIONS
OSCILLATOR
ELEMENT
--"
1.8432
Mhz
EIA
EIA
RECEIVERS
DRIVERS
A
CURRENT
LOOP
Y
~
A
L
J
L.
25
PIN
"D"SHELLCONNECTOR
Figure
22.
ASYNCHRONOUS
COMMUNICATIONS
ADAPTER
BLOCK
DIAGRAM
2-124
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