XR88C681J-F Datasheet, PDF (7/101 Pages) Exar Corporation – Two Full Duplex, Independent Channels

XR88C681
44 PLCC
38
40 PDIP,
CDIP
34
39
35
40
36
41
37
41
37
42
38
42
38
43
39
43
39
44
40
28 PDIP
25
26
27
28
Symbol Type Description
RESET
-CS
IP2
(C/T_EX)
IP6
(RXCB)
-IACK
IP5
(TXCB)
IEO
(Z-Mode)
IP4
(RXCA)
IEI
(Z-Mode)
V_CC
I
I
I
I
I
I
O
I
I
PWR
Master Reset (Active High). Asserting this input clears in-
ternal registers, SR, ISR, IMR, OPR, OPCR, and initializes
the IVR to 0F16. Asserting this input also stops the Counter/
Timer, puts OP0 - OP7 in the high state, and places both
serial channels in the inactive state with TXDA and TXDB
outputs marking (high).
Chip Select (Active Low). The data bus is tri-stated when
-CS is “high.” Data transfers between the CPU and the
DUART via D0 - D7 are enabled when -CS is “low”.
Input 2. (General Purpose Input). This input pin can also
be programmed to function as the “Counter/Timer external
clock” input (C/T_EX).
Input 6 (I-Mode). General Purpose Input pin. This input pin
can also be programmed to function as the External Receiv-
er Clock for Channel B (RXCB).
Interrupt Acknowledge Input (Z-Mode). Active Low.
This input is the CPU’s response to the Interrupt Request
issued by the DUART device. When the CPU asserts this
input, it indicates that the DUART’s interrupt request is about
to be serviced, and that the very next cycle will be an Inter-
rupt Acknowledge Cycle. The DUART will respond to the
CPU’s Interrupt Acknowledge by placing the contents of the
Interrupt Vector Register (IVR) on the data bus (D0 - D7).
Input 5 (I-Mode). General Purpose Input pin. This pin can
also be configured to function as the external clock input for
the Transmitter of Channel B (TXCB).
Interrupt Enable Output (Z-Mode). Active High.
This output pin is normally “high”. However, either of the
following two conditions can cause this output pin to be ne-
gated (toggled “low”).
1. If the IEI (Interrupt Enable Input) pin is “low”. If IEO is
“low” because of the IEI pin, IEO will toggle “high” once
the IEI has toggled “high”.
2. The DUART has issued an Interrupt Request to the CPU
(-INTR pin is toggled “low”). If IEO is “low” because the
DUART has requested an Interrupt, then IEO will remain
“low”, throughout the Interrupt Service Routine, until the
CPU has invoked the “” command.
Input 4 (I-Mode). General Purpose Input pin. This input pin
can also be configured to function as the external clock input
for the Receiver of Channel A (RXCA).
Interrupt Enable Input (Z-Mode). Active High.
If this active-high input is at a logic “high”, the DUART is ca-
pable of generating all non-masked Interrupt Requests to the
CPU. If this input is at a logic “low”, the DUART is inhibited
from generating any Interrupt Requests to the CPU.
Most Positive Power Supply.
Rev. 2.11
7