Modes: The BD429 operates in either a 429 mode or a 422 mode as controlled by the 429/422´ pin.
429 Mode: In 429 mode, the serial data is presented on the DATA(A) and DATA(B) inputs in the dual rail
format defined in the MARK 33 Digital Information Transfer System – ARINC Specification 429-10. The
driver is enabled by the SYNC and CLOCK inputs. The output voltage level is programmed by the VREF
input and is normally tied to +5VDC along with V1 to produce output levels of +5 volts, 0 volts, and –5
volts on each output for ±10 volts differential outputs. *See figure 2.
422 Mode: In 422 mode, the serial data is presented on DATA(A) input. The driver is enabled by the
SYNC and CLOCK inputs. The outputs swings between 0 volts and +5 volts if VREF is at +5VDC. *See
Output Resistance: The driver output resistance is 75Ω ±20% at room temperature; 37.5Ω on each out-
put. The outputs are also fused for failsafe protection against shorts to aircraft power. The output slew
rate is controlled by external timing capacitors on CA and CB. Typical values are 75pF for 100 KHz data
and 500pF for 12.5 KHz data.
Table 2: Pin Descriptions
Analog Input. The voltage on VREF sets the output voltage levels on AOUT and BOUT. The output
logic levels swing between +VREF, 0 volts, and –VREF volts.
NC No Connect
Logic input. Logic 0 forces outputs to NULL state. Logic 1 enables data transmission.
Logic inputs. These signals contain the Serial Data to be transmitted on the ARINC 429 data bus.
Refer to Figures 2 and 3.
Analog Nodes. External timing capacitors are tied from these points to ground to establish the out-
put signal slew rate. Typical CA = CB = 75pF for 100 kHz data and CA = CB = 500pF for 12.5 kHz
Outputs. These are the line driver outputs which are connected to the aircraft serial data bus.
-V Negative Supply Input. –15VDC nominal.
+V Positive Supply Input. +15VDC nominal.
CLOCK Logic input. Logic 0 forces outputs to NULL state. Logic 1 enables data transmission.
Logic Input. Mode control for ARINC 429 and RS-422 modes. An internal 10KΩ pull up resistor
keeps the chip in ARINC 429 mode when there is no external connection. This creates a default
logic 1, enabling the ARINC 429 mode. A forced logic 0 enables the RS-422 mode.
V1 Logic Supply Input. +5VDC nominal.
*CA and CB pin voltages swing between ±5 volts. Any electronic switching of the capacitor on the pins must not inhibit the full voltage swings.
© 1999 Device Engineering Inc.
430 S. Rockford Tempe, AZ 85281
2 of 11
BD429 Rev. B
March 24, 2000