COM90C66 Datasheet, PDF (4/76 Pages) SMSC Corporation – ARCNET Controller/Transceiver with AT Interface and On-Chip RAM

PLCC
PIN NO.
NAME
75-84, 2- Address 0-19
11
13-20, Data 0-15
22-29
63, 62
nTransceiver
Direction
Control
71 I/O Channel
Ready
12 Address
Enable
74 Address Latch
Enable
64 nI/O Read
65 nI/O Write
DESCRIPTION OF PIN FUNCTIONS
SYMBOL
DESCRIPTION
PROCESSOR INTERFACE
A0-A19
Input. These signals are connected to the address lines
of the host processor and are used to access memory
and I/O locations of the COM90C66, as well as to access
the external ROM through the COM90C66.
D0-D15
Input/Output. These signals are used by the host to
transmit data to and from the internal registers and buffer
memory of the COM90C66 and are connected to weak
internal pull-up resistors.
nTOPL,
nTOPH
Output. These active low signals control the data bus
transceiver. When these signals are high, data gets sent
from the PC to the COM90C66. When these signals are
low, data gets sent from the COM90C66 to the PC, or
from the PROM to the PC if the PROM signal is also low.
IOCHRDY
Output. This signal, when low, is optionally used by the
COM90C66 to extend host cycles. This is an open-drain
signal. An external pull-up resistor is typically provided
by the system.
AEN
Input. This signal, when low, acts as a qualifier for I/O
Address Selection. When the signal is high, I/O
decoding is disabled. This signal has no effect on
Memory Address Selection.
BALE
Input. The falling edge of this signal is used by the
COM90C66 to latch the A0-A19 lines and the nSBHE
signal via an internal transparent latch. This signal is
connected to a weak internal pull-up resistor.
nIOR
Input. This active low signal is issued by the host
microprocessor to indicate an I/O Read operation. A low
level on this pin when the COM90C66 is accessed
enables data from the internal registers of the
COM90C66.
nIOW
Input. This active low signal is issued by the host
microprocessor to indicate an I/O Write operation. A low
pulse on this pin when the COM90C66 is accessed
enables data from the Data Bus into the internal registers
of the COM90C66.
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