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CT 9000 ® ADV
3-20
output lines (OP1, OP3-OP5) are used to control LED's.
A high on
these outputs will drive the output of the 74LS05, U11, low, thereby
pulling current through the current limiting resistors, R13-R16, and
the LED's, LED1-LED4.
Output OP6 provides on/off control for the
RS-422 line driver, U20.
Output OP7 provides on/off control for the
RS-422 line receiver, Ui9. LED1-LED4 are for programming and
are not used for data during normal operation.
The interrupt line for DUART U14 is connected to IRQ5 on the
microprocessor and the chip select is connected to CS8 on the
microprocessor.
The transmit outputs of U14 are connected to a 34C87, U20 pin 9
and 15, which is a quad RS-422 line driver. The outputs of each
driver has a 10y series resistor and an EMI filter on each differential
output.
As mentioned above, on/off control for this chip is provided
by OP6.
The receive inputs are connected to a 34C86, U19 pin 3
and 5, which is a quad RS-422 line receiver. A 220y resistor is
placed across the differential inputs. As mentioned above, on/off
control for this chip is provided by OP7.
The following discussion will refer to DUART U13.
All 6 input lines
(IPO-IP5) all 8 output lines (OPO-OP7) and both pairs of receive
and transmit lines are output to connector K1, K9, K10, K11.
A 3.6864 MHz crystal (X2) is used by U13 to generate standard bit
rates.
The interrupt line for DUART U13 is connected to IRQ6 on the
microprocessor and the chip select is connected to CS6 on the
microprocessor.
Auxiliary RS-422 Inputs
Two line receivers U19 pins 1 and 13 are used both as inputs to a
microprocessor I/O pin and as input to IRQ7, the non-maskable
interrupt. The output of the two line receivers are input to an RC
network—R45, C29 and R46, C80—and then to open collector
inverters, U11.
When the output of the line receiver goes low the
RC network generates a pulse into the open collector inverter. This
prevents the NMI line from bouncing and from staying low indefi-
nitely. The output of these two open collector gates are then tied
together, pulled up by RN5 and input to IRQ7.
EEPROM Operation
The EEPROM (U17) is socketed so that either an 8K x 8-bit or 32K
x 8-bit EEPROM can be used.
No modification is necessary to
move from one size to the other.
The R/W line is inverted by U9 pin 6 to generate the EEPROM
output enable (OE).
800961-C
Nov. 2000
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