XRT79L74 Datasheet, PDF (6/70 Pages) Exar Corporation – 4 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC

XRT79L74
REV. P1.0.0
PRELIMINARY
4 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC
PIN DESCRIPTIONS
PIN #
NAME
TYPE
DESCRIPTION
MICROPROCESSOR INTERFACE
AB26
A0
AC26
A1
AD26
A2
AB25
A3
AA24
A4
AD25
A5
AC25
A6
AB24
A7
AF25
A8
AE25
A9
AF24
A10
AE24
A11
AD24
A12
AC24
A13
AF23
A14
I Address Bus Input pins Microprocessor Interface:
These direct address pins are used to select the on-chip Framer/UNI registers and
RAM space for READ and WRITE Operations with the Microprocessor.
R22
D0
I/O Bi-Directional Data Bus pins Microprocessor Interface:
T24
D1
These pins are used to drive and receive data over the bi-directional data bus.
T25
D2
T26
D3
U22
D4
U23
D5
U24
D6
U25
D7
AB23
ALE/AS
I Address Latch Enable/Address Strobe:
This input pin is used to latch the address present at the Microprocessor Interface
Address Bus pins A[14:0] into the Framer/UNI Microprocessor Interface block and to
indicate the start of a READ or WRITE cycle. This input pin is active high, in the Intel
Mode and active low in the Motorola Mode.
AE23
CS
I Chip Select Input:
The user must assert this active low signal in order to select the Microprocessor
Interface for READ and WRITE operations between the Microprocessor and the UNI/
Framer on-chip registers and RAM locations.
R23
INT
O Interrupt Request Output:
This open-drain, active-low output signal will be asserted when the Framer/UNI
device is requesting interrupt service from the Microprocessor. This output pin
should typically be connected to the Interrupt Request input of the Microprocessor.
AD23
RD/DS
I READ Strobe Intel Mode:
If the Microprocessor Interface is operating in the Intel Mode, then this input pin will
function as the RD (READ Strobe) input signal from the Microprocessor. Once this
active-low signal is asserted, then the Framer/UNI will place the contents of the
addressed register within the Framer/UNI IC on the Microprocessor Bi-directional
Data Bus D[7:0]. When this signal is negated, the Data Bus will be tri-stated.
Data Strobe Motorola Mode:
If the Microprocessor Interface is operating in the Motorola Mode, then this input will
function as the DS (Data Strobe) signal.
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