TILT400 serial4

The Systronix TILT400Pro socket board is designed to make available on a D-sub connector the third on-board serial port, serial4, that is available on SNAP and TStik, but not on TINI390. However, because of the differences between SNAP and TStik, the serial4 connector on a TILT400Pro board does not work with SNAP without modification of the socket board. This document deals with this issue.

1 Differences between SNAP and TStik

TStik uses serial1 to communicate with the DS2480 chip that controls the external 1-wire bus, while SNAP uses serial4 for the same purpose. When the external 1-wire bus is used, the serial port associated with it can not be used as a serial (RS-232) port by the user program.

There is an input in the SNAP/TStik edge connector called EN2480 that is used to select between use of external 1-wire bus or serial port. When this input is set high, 1-wire is selected and the associated serial port is disabled for other use.

The designers of the TILT400Pro assumed that almost all users would need an external 1-wire bus, and/or that almost all users would need no more than two serial ports. With this in mind, they left the EN2480 signal open (which will make it go high) and pulled serial0 and serial4 out to connectors. But when EN2480 is high, serial4 on the SNAP is disabled, and its fully-functional serial1 port is not tied to any connector.

This makes it necessary to modify the TILT400Pro board in one of the two ways described below in order to make full use of it together with the SNAP.

2 Enabling serial4 by pulling EN2480 low

If EN2480 (pin 26) is pulled low, the serial4 port on the SNAP will be enabled. This can be accomplished by soldering a wire on the bottom side of the TILT400Pro board from pin 26 in the 72-pin SIMM socket to any signal ground point - for example pin 3 of the same connector.

The advantage of this method is that it will also allow use of a TStik module in the modified socket board, but the of course the external 1-wire bus will not work.

3 Enabling serial1 instead

When the EN2480 pin is left open or tied high, the SNAP serial4 port is disabled and both its signals (pins 4,5) are tristated. This opens up the possibility to instead route serial1 to the level shifter and connector on the socket board that were meant for serial4. All that is needed is to connect the serial1 signals (pins 14,15) to the tristated serial4 signals (pins 4,5). See image below.

The effect of this will be that serial1 is available on the top D-sub connector on the TILT400Pro instead of serial4. External 1-wire will still be available.

With this modification, a TStik module should not be used, since its serial1 (used for 1-wire) and serial4 ports will be driving against each other with unpredictable results.

4 Modification done before delivery

The modification described in section 3 is preferred, and it is also done on all TILT400Pro boards delivered from Imsys Technologies since May 2005. These boards have the marking on the top side changed from "Serial4" to "Serial1", see picture.

On a TILT400Pro board purchased recently from Imsys Technologies web shop no modifications are necessary to make serial0, serial1 and external 1-wire available all at the same time.

TILT400Pro boards purchased earlier, or purchased from other sources than Imsys Technologies web shop, will have to be modified by the customer in one of the ways described above, otherwise the top D-sub connector will be disabled and only one serial port (serial0) will be available with SNAP.