Major Chips Description 2-85
Table 2-14 NS87336VJG Pin Descriptions (continued)
Pin No. I/O Description
/RI1
/RI2 68, 60 IUARTs Ring Indicator. When low, this indicates that a telephone ring
signal has been received by the modem. The /RI signal is a modem
status input whose condition is tested by the CPU by reading bit 6
(RI) of the Modem Status Register (MSR) for the appropriate serial
channel. Bit 6 is the complement of the RI signal. Bit 2 ( TERI) of
the MSR indicates whether the RI input has changed from low to high
since the previous reading of the MSR.
NOTE: When the TERI bit of the MSR is set and Modem Status
interrupts are enabled, an interrupt is generated.
/RTS1
/RTS2 72, 64 OUARTs Request to Send. When low, this output indicates to the
modem or data set that the UART is ready to exchange data. The
RTS signal can be set to an active low by programming bit 1 (RTS) of
the Modem Control Register to a high level. A Master Reset
operation sets this signal to its inactive (high) state. Loop mode
operation holds this signal to its inactive state.
SIN1
SIN2 73, 65 IUARTs Serial Input. This input receives composite serial data from
the communications link (peripheral device, modem, or data set).
SIRQ1
SIRQ2
SIRQ4
58,
49,
47
ISystem interrupt 1, 2, and 3. This input can be routed to one of the
following output pins: IRQ3-IRQ7, IRQ9-IRQ12. SIRQ12 and
SIRQ13 can be also routed to IRQ15. Software configuration
determines to which output pin the input pin is routed to.
SIRQ1 is multiplexed with IRQ15, SRIQ12 is multiplexed with
DRATE1/MSEN1/CS0, and SIRQ3 is multiplexed with
DRV2/PNF/DR23.
SLCT 80 IParallel Port Select. This input is set high by the printer when it is
selected. This pin has a nominal 25 KΩ pull-down resistor attached
to it.
/SLIN 79 I/O Parallel Port Select Input. When this signal is low, it selects the
printer. This pin is in a tristate condition 10 ns after a 0 is loaded into
the corresponding Control Register bit. The system should pull this
pin high using a 4.7 KΩ resistor.
SOUT1
SOUT2 71, 63 OUARTs Serial Output. This output sends composite serial data to the
communications link (peripheral device, modem, or data set). The
SOUT signal is set to a marking state (logic 1) after a Master Reset
operation.
/STB 93 I/O Parallel Port Data Strobe. This output indicates to the printer that a
valid data is available at the printer port. This pin is in a tristate
condition 10 ns after a 0 is loaded into the corresponding Control
Register bit. The system should pull high using a 4.7 KΩ.
/STEP
(Normal Mode) 38 OFDC Step. This output signal issues pulses to the disk drive at a
software programmable rate to move the head during a seek
operation.
/STEP
(PPM Mode) 79 OFDC Step. This pin gives an additional step signal in PPM Mode
when PNF = 0.