Honeywell bendis king KLN 94 Maintenance Manual page 39

BENDIX/KING
Level shifter transistors Q5008 and Q5011 permit the standard 5V logic of the Host microproces-
sor to connect the drive transistors to the -12V supply rail during the active low state. Resistors
R5136, R5140, R5006, R5141, R5145, R5147 and R5146 supply the needed bias currents.
Clamp transistor Q5005 is turned on by the GRAPHICS_RESET signal to prevent bursts of light
during that period of start-up when the microprocessor is not initialized.
Driver transistors Q5003 and Q5007 buffer PWM drive signal DISPLAY_LED_PWM. Resistors
R5009, R5135, R5138, and R5139 dampen high current noise transients. The buffered PWM sig-
nal drives the gates of Q5004 which causes the display backlighting LEDs to turn on during that
portion of the PWM cycle when Q5004 is active.
4.3.4.2.34 Discrete Inputs
U5015 and U5005 are parallel-to-serial shift registers which are daisy chained together. Discrete
Main Board signals and flags are sent to the Host microprocessor via a serial peripheral bus. They
are read in using SCLK while the DISCRETE_IN_SELECTn is signal held low.
4.3.4.2.35 Gillham Altitude Inputs
The KLN 94 has the capacity for ten Gillham Altitude Inputs, as well as, other discrete inputs. As
these circuits are functionally identical, only the operation of the Gillham Input D4 will be dis-
cussed. U5035 translates the input voltage to a digital logic level which is applied to the Main mi-
croprocessor data bus when DISCRETE_CS2_RDn is asserted low. C5232 is used for EMI pro-
tection.
4.3.4.2.36 Configuration Module
The Configuration Module contains an EEPROM which stores some of the system configuration
information for the KLN 94. The Module is housed in the mounting rack for the KLN 94 and con-
tains a 256-bit EEPROM (U7001) which is communicated to in a serial manner. Signals
EXT_EEPROM, EXT_EEPRM_CS, Serial_OUT_OBI_DATAn, Serial_IN and Serial_CLK run
through the J5006 connector to the Power Board to J943.
4.3.4.2.37 OBI Serial Bus Driver
The OBI_DATA, OBI_CLOCK, and OBI_SYNC signals are created using the latched outputs of
U5023. As all three are identical, only the OBI_DATA circuit will be described here. Driver FET
Q5038 is driven via R5046. When the gate of Q5038 is driven high, the drain pin will be pulled
near 0V. Current limit resistor R5053 and clamp diode CR5014 provide lightning protection.
When a high voltage pulse appears on Q5038's drain, CR5014 clamps the gate-source voltage.
This causes Q5038 to momentarily shut off, preventing damage.
Page 4-40 15599M00.JA
KLN 94
Rev 0, Sept/2000