COM90C66 Datasheet, PDF (5/76 Pages) SMSC Corporation – ARCNET Controller/Transceiver with AT Interface and On-Chip RAM

DESCRIPTION OF PIN FUNCTIONS
PLCC
PIN NO.
NAME
SYMBOL
DESCRIPTION
66 nMemory Read nMEMR
Input. This active low signal is issued by the host
microprocessor to indicate a Memory Read operation. A
low level on this pin when the COM90C66 is accessed
enables data from the internal RAM of the COM90C66 or
the PROM onto the data bus to be read by the host.
67 nMemory
Write
nMEMW
Input. This active low signal is issued by the host
microprocessor to indicate a Memory Write operation. A
low pulse on this pin when the COM90C66 is accessed
enables data from the data bus into the internal RAM of
the COM90C66.
52 Reset In
RESETIN
Input. This active high signal is the power on reset signal
from the host. It is used to activate the internal reset
circuitry within the COM90C66.
53 nROM Enable nENROM Input. This active low signal enables the decoding of the
external PROM. This signal also affects the timing of
IOCHRDY and the number of address lines used to
decode nMEMCS16. This signal is connected to a weak
internal pull-up resistor.
54 nROM Select nPROM
Output. This active low signal is issued by the
COM90C66 to enable the external 8-bit wide PROM or
the external register of the COM90C66.
30 Interrupt
Request
INTR
Output. This active high signal is generated by the
COM90C66 when an enabled interrupt condition occurs.
INTR returns to its inactive state when the interrupt
status condition or the corresponding interrupt mask bit
is reset.
72 nZero Wait
State
n0WS
Output. This active low signal is used to force zero wait
state access cycles on the IBM PC Bus. This is an open-
drain signal. An external pull-up resistor is typically
provided by the system.
70 nMemory
16-Bit Chip
Select
nMEMCS16
Output. This active low signal is used to indicate that the
present data transfer is a 16-bit memory cycle. The
COM90C66 can be configured to use A19-A17 or A19-
A11 to generate nMEMCS16. This is an open-drain
signal. An external pull-up resistor is typically provided
by the system.
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