Slave Bus Terminator

The Slave Bus Terminator (also known as the IIC Active Terminator) solves some problems with Avionics display glitches. Avionics stacks prior to March 2010 did not include a terminator. This page explains how to install one.





Installing the Slave Bus Terminator on a USB Wide Stack


USB_avionics_wide_stack_800x.JPG (689.91 Kb)

Above is a typical USB wide stack. Ideally we'd like the terminator to be at the end of the cable farthest away from the motherboard. On the wide stack the cable starts at the bottom left, goes up the left side, then down the right side to end at the DME panel. Below you can see the back of the removed DME panel and the end of the cable.

NOTE: Unplug the power from your stack before working on it!

DME_0.jpg (535.57 Kb)

DME_1.jpg (337.95 Kb)

Remove the ribbon cable from the connector and add the terminator. Please note that the terminator can only be installed one way; if you install it upside-down it will destroy the terminator and may possibly damage other parts of your stack! You should be able to read the silkscreened board numbers right-side-up. For example, the DME board is 560002-01 and is located at the bottom left of the board in the photo; the slave board number is 400001-01 (bottom right of the slave board) and the terminator board is 630001-01 (top of the board among the pins of one connector and above the other). Another way to tell is to note that the terminator is designed to hang down over the slave board, not stick up above it.

WRONG!
DME_2_bad.jpg (86.03 Kb)

Right!
DME_3_good.jpg (354.27 Kb)

Now plug the cable in the same way it was plugged in before.
  • The stripe should be on the left, closest to pin 1.
  • The key should be down (towards the center of the slave board, away from the edge)
  • The connector will have a small mark, usually an arrow, that designates pin 1.

Below is a photo of a typical connector:
conn.jpg (71.52 Kb)

Note the reddish stripe along the length of the wire on the left:

DME_4.jpg (330.95 Kb)

Newer Avionics stacks may use what we call the USB Slave Board. The instructions are the same as for the older slave board though the connector is in a different position.

Before:
DME_5.jpg (339.02 Kb)

After:
DME_6.jpg (374.35 Kb)



Results

For your erudition and entertainment here are some before-and-after captured waveforms. Ideally the signals should be nice and clean, with fast-rising edges and squared-off corners. The shark-fin shapes of the following signals are marginal at best:

term_new_before.png (57.83 Kb)


This is what the signals look like with the terminator. The small spikes at the corners and other irregularities are imperfections but will not harm anything.

term_new_after.png (50.38 Kb)


Installing the Slave Bus Terminator on a Serial Avionics Stack


avionics.png (589.32 Kb)

Above is a typical serial Avionics stack. Ideally we'd like the terminator to be at the end of the cable farthest away from the motherboard. On the serial stack the cable starts at the bottom and goes up to the top to end at the NAV1 panel. Below you can see the back of the removed COM1/NAV1 panel and the end of the cable.

NOTE: Unplug the power from your stack before working on it!

COMM_1.jpg (343.88 Kb)

COMM_2.jpg (369.96 Kb)

Remove the ribbon cable from the connector and add the terminator. Please note that the terminator can only be installed one way; if you install it upside-down it will destroy the terminator and may possibly damage other parts of your stack! You should be able to read the silkscreened board numbers and other text right-side-up. For example, the NAV1 board has the text "Manufactured by PuSH Inc" located at the bottom left of the board in the photo; the slave board number is 400001-01 (bottom right of the slave board) and the terminator board is 630001-01 (top of the board among the pins of one connector and above the other). Another way to tell is to note that the terminator is designed to hang down over the slave board, not stick up above it.

WRONG!
COMM_3_bad.jpg (85.93 Kb)

Right!
COMM_4_good.jpg (374.33 Kb)


Now plug the cable in the same way it was plugged in before.
  • The stripe should be on the left, closest to pin 1.
  • The key should be down (towards the center of the slave board, away from the edge)
  • The connector will have a small mark, usually an arrow, that designates pin 1.

Below is a photo of a typical connector:
conn.jpg (71.52 Kb)

Note the reddish stripe along the length of the wire on the left:

COMM_5.jpg (377.27 Kb)


Results

For your erudition and entertainment here are some before-and-after captured waveforms. Ideally the red trace should look more like the blue trace, with fast-rising edges and squared-off corners.

serial_avi_stack_without_2.jpg (35.93 Kb)

Unfortunately it doesn't. But with the new terminator board they look more like this:

serial_avi_stack_with_2.jpg (37.71 Kb)

The glitches have turned into spikes, which is unfortunate but doesn't actually hurt anything. But the important thing is that the legitimate signals rise quickly and provide consistent and reliable communications.


Installing the Prototype Slave Bus Terminator on a Serial Avionics Stack

Slavebus_terminator_prototype.jpg (47.76 Kb)
This is the prototype of a new Slave Bus Terminator that will improve the reliability of PFC serial Avionics stacks.

Here's a typical serial Avionics stack.
avionics.png (589.32 Kb)

Detail view of the terminator prototype:
Slavebus_terminator_prototype_closeup.jpg (86.41 Kb)

Note the black marker on one corner of each connector (one is next to the green wire on the left). It should be on the same side of the board as the stripe on the ribbon cable, as shown.

Instructions

1. Unscrew four Phillips screws holding in the COM1/NAV1 panel at the top of the stack. (If the top panel is not COM1/NAV1, unscrew the top panel anyway.)
2. Locate the end of the ribbon cable. See the photo below, right side:

CableEnd.jpg (88.44 Kb)

This photo is typical but your installation may vary. For example, the end of the cable does not have to be on the NAV1 panel. It is ideal but not critical that the terminator be placed at the end of the cable.

3. Carefully pull the panel out but try not to unplug the non-end connector. Note the orientation of the stripe on the cable.
4. Unplug the end connector.
5. Plug in the terminator board.
6. Plug the cable end connector into the terminator board. It should look something like this:

Slavebus_terminator_prototype_installed.jpg (63.71 Kb)

Note that the stripes on the ribbon cables line up the same the entire way through and the new cable is oriented the same as the old cable.

7. Stuff the wires (including the terminator) back into the Avionics case, replace the panel, and screw it back down.

Results

For your erudition and entertainment here are some before-and-after captured waveforms. Ideally the red trace should look more like the blue trace, with fast-rising edges and squared-off corners.

serial_avi_stack_without_2.jpg (35.93 Kb)

Unfortunately it doesn't. But with the new terminator board they look more like this:

serial_avi_stack_with_2.jpg (37.71 Kb)

The glitches have turned into spikes, which is unfortunate but doesn't actually hurt anything. But the important thing is that the legitimate signals rise quickly and provide consistent and reliable communications.