
XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
PRELIMINARY
REV. P1.1.1
15
PIN DESCRIPTION
P
IN
#
N
AME
T
YPE
D
ESCRIPTION
Microprocessor Interface
AB3
AA4
AA1
AA2
Y1
Y2
Y3
A0
A1
A2
A3
A4
A5
A6
I
Address Bus Input (Microprocessor Interface):
These pins are used to select the on-chip Framer/UNI registers and RAM space
for READ/WRITE operations with the “l(fā)ocal” microprocessor.
V4
NibbleIntf
I
Nibble Interface Select Input pin:
This input pin permits the user to configure the Transmit Payload Data Input
Interface and the Receive Payload Data Output Interface blocks to operate in
either the "Serial" or the "Nibble-Parallel" Mode.
Setting this input pin "high" configures each of these blocks to operate in the Nib-
ble-Parallel Mode. In this mode, the "Transmit Payload Data Input Interface"
block will accept the "outbound" payload data (from the local terminal equip-
ment) in a "nibble-parallel" manner via the "TxNib[3:0]" input pins. Further, the
Receive Payload Data Output Interface block will output "inbound" payload data
(to the local terminal equipment) in a "nibble-parallel" via the "RxNib[3:0] output
pins.
Setting this input pin "low" configures each of these blocks to operate in the
Serial Mode. In this mode, the Transmit Payload Data Input Interface block will
accept the "outbound" payload data (from the local terminal equipment) in a
"serial" manner via the "TxSer_n" input pin. Further, the Receive Payload Data
Output Interface block will output the "inbound" payload data (to the local termi-
nal equipment) in a serial manner, via the "RxSer_n" output pin.
N
OTE
:
This input pin is only active if the XRT74L74 device has been configured
to operate in the Clear-Channel Framer Mode.
AC7
AD6
AE5
AF4
AC5
AD4
AE3
AF2
D0
D1
D2
D3
D4
D5
D6
D7
I/O
Bi-Directional Data Bus (Microprocessor Interface Section):
These pins function as the Microprocessor Interface bi-directional data bus and is
intended to be interfaced to the “l(fā)ocal” microprocessor. This pin is inactive if the
Microprocessor Interface block is configured to operate over an 8 bit data bus.
AE2
ALE_AS
I
Address Latch Enable/Address Strobe:
This input is used to latch the address (present at the Microprocessor Interface
Address Bus, A[6:0]) into the Framer/UNI Microprocessor Interface circuitry and
to indicate the start of a READ or WRITE cycle. This input is active-"High" in the
Intel Mode (MOTO = “Low”) and active-”Low” in the Motorola Mode (MOTO =
“High”).
Chip Select Input:
This active-”Low” input signal selects the Microprocessor Interface Section of the
UNI/Framer and enables Read/Write operations between the “l(fā)ocal” micropro-
cessor and the UNI/Framer on-chip registers and RAM locations.
AB1
CS
I