XR88C681_06 Datasheet, PDF (27/101 Pages) Exar Corporation – CMOS Dual Channel UART (DUART)

XR88C681
-INT0
-RD
-WR
PORT 0
(AD0 - AD7)
ALE
PORT 2
(A8 - A15)
8051 CPU
74HC373
D
Q
C
A0 - A3
A5 - A7
Address
Decoding
Logic
CS_DUART
to other ICs
-INTR
-RD
-WR
D0 - D7
A0 - A3
-CS
XR88C681
Figure 5. An Approach to Interfacing the XR88C681 DUART to the 8051 Microcontroller
The circuitry presented Figure 5 would function as follows
during a DUART requested interrupt. The DUART device
requests an interrupt from the CPU by asserting its active
low -INTR output pin. This will cause the -INT0 input pin to
the CPU to go low. When this happens the 8051 CPU will
finish executing its current instruction, and will then
branch program control to the DUART interrupt service
routine. In the case of Figure 5, since the DUART’s -INTR
pin is tied to the -INT0 pin of the C, then the beginning of
the interrupt service routine will be located in 0003H in
code memory. The 8051 CPU does not issue an Interrupt
Acknowledge signal back to the DUART. It will just begin
processing through the DUART’s interrupt service
routine. Once the CPU has eliminated the cause(s) of the
interrupt request, the DUART’s -INTR pin will be negated
(go “high”) and the CPU will return from the interrupt
service routine and resume normal operation.
C.6.1.2 8080A Microprocessor
The 8080A Microprocessor is one of the earlier version of
the Intel processors. In general, it is an 8-bit
microprocessor that requires +5V, -5V, and +12V power
supplies. Additionally, this microprocessor requires two
other chips, in order to create a “complete” CPU module.
Typically, these devices would be the 8224 Clock
Generator and the 8228 System Controller. The 8224
Clock Generator is responsible for conditioning and
generating the necessary timing source for the 8080A
Rev. 2.11
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