Section 4
FUNCTIONAL
4
DESCRIPTION
page 4.7
RCP–48X
Functional
cycle at address 800h, the CPU can determine the state of pushbuttons
S1-S8 by looking at the state of data bits D0-D7. If S1 is pressed, then D0
will be low. Likewise, if S2 is pressed, D1 will be low. The status of the
entire keyboard array may be determined by performing successive reads
of each row of the array.
LED Driver
The RCP–48X switchcard contains circuitry capable of lighting up to 68
LEDs. The RCP–48X uses only 50 of these LEDs, one per pushbutton.
The drive for each LED is provided by U1or U2. The CPU sends a serial
data stream to U1 and U2 by using the LED_DATA (pin 25) and
LED_CLOCK (pin 24) signals. LED_SEL0 (U1 pin 26) must be asserted
(low active) to update LEDs 1-34. Likewise, LED_SEL1 (U2 pin 26) must
be asserted to update LEDs 35-50. The output current used to drive each
LED is enabled by the brightness pin of the LED driver (pin 21). The
LED_DATA line is latched into U1 and U2 on the rising edge of
LED_CLOCK while LED_SEL0 or LED_SEL1 is asserted.
I/O Board Interface
Connector J3 provides the signals necessary to interface to an optional
I/O board. The connector pr5 Vdc (pin 1) and ground (pin 6) to
power the external board. In addition, data bit D0 (pin 2), address bit A0
(pin 3), and chip select SEL5 (pin 4) are present on the connector. Pin 5 of
the connector is connected to ID0, and is used to detect the presence or
absence of the external board (see Switchcard ID, above).
Switchcard Continued:
