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F UNCTIONAL
4
DE SCRIPTI ON
Section 4
Functional
RCP-GPIO
Although the GPIO Interface Card only uses rows 0-3, the microprocessor
still scans all 16 rows. Each row of push-buttons contains up to eight indi-
vidual switches.
Example:
KB_ROW0 will simultaneously enable inputs 1-
8. If any of these inputs are activated, the active low signal will be passed
through the input jumpers to one of the eight column signals (KB_COL0
through KB_COL7). If the input is not activated the column signal will be
pulled high by resistor pack RP1. The KRD_SEL signal also enables U1 to
place the KB_COL signals on the data bus. Thus, by performing a read
cycle at address 800h, the microprocessor can determine the state of in-
puts 1-8 by looking at the state of data bits D0-D7. If input 1 is activated,
then D0 will be low. Likewise, if input 2 is activated, D1 will be low. The
status of the entire input array may be determined by performing succes-
sive reads of each row of the array.
Output Relay Activation
While the GPIO Interface Card contains circuitry capable of activating up
to 34 output relays, the GPIO only uses 32 of the output relay driver cir-
cuits (one per output). The drive for the output relay circuits is provided by
U36 (MM5450V LED Driver). The microprocessor sends a serial data
stream to the MM5450V LED driver using the LDATA (pin 25 of LED
driver chip) and LCLK (pin 24 of the LED driver chip) signals. The enable
signal (pin 26 of the LED driver chip) is always asserted (active low). The
output current used drive each LED is enabled by the brightness pin of the
LED driver (pin 21). Resistor R323 sets the current flow through the output
relays. The LDATA line is latched into the LED driver chip on the rising
edge of LCLK.
4.2 GPIO Interface Card Continued:
Inputs Scan Continued:
