Scenix SX Programming Connector

Editor's note, 27-JAN-1998:

The following was written by Richard Ottosen in response to difficulties with Revision C of the Parallax SX-Key. The transition from programming mode to run mode has reportedly been improved in the Revision E SX-Key, such that a separate MCLR* signal may not be necessary. Parallax has been shipping the Revision E SX-Key for quite some time now.

The SX-Key does not always give a good reset to the SX after programming it. From now on SX circuits will use the following pinout for the programming connector:

Pin Function
1 MCLR*
2 (key, reserved for future use)
3 OCS1
4 OSC2
5 VDD
6 VSS

Pin	Function
1	MCLR*
2	(key, reserved for future use)
3	OCS1
4	OSC2
5	VDD
6	VSS

This pinout assumes that the MCLR* pin of the SX is pulled up to +5 volts through a 10K ohm resistor.

It is expected that all future developement systems will also have this 6 pin connector.

A reset circuit can be added to the SX programming circuit using a 6.2 volt zener diode, a 47K ohm resistor and an N-channel VMOS FET. Connect the cathode of the zener to the OSCI pin of the SX. Connect the anode to one end of the resistor and the gate of the FET. Connect the other end of the resistor and the source of the FET to ground. Connect the drain of the FET to the MCLR* pin of the SX.

Adding a programming connector to a prototype circuit using an 18 pin SX is easy. Use a right angle 6-pin SIP header. Remove pin 2 and straighten pins 1 and 6. Align the connector with the 6 pins over pins 13 through 18 of the SX with the empty position over pin 17 of the SX. The three right angle pins of the connector solder in order to pins 16, 15 and 14 of the SX on the circuit side of the PCB. Jumper from the connector pin above pin 13 to pin 5 (ground) of the SX. Jumper the pin above pin 18 to pin 4 (MCLR*) of the SX.

You can also build a "development system" SX by soldering a connector directly to an SX designated for testing. Use a right angle 6-pin SIP header. Remove pin 2 and straighten pins 3, 4 and 5. Align the connector with the 6 pins over pins 13 through 18 of the SX with the empty position over pin 17 of the SX. The three straight pins of the connector solder in order to pins 16, 15 and 14 of the SX. Jumper from the connector pin above pin 13 to pin 5 (ground) of the SX. Jumper the pin above pin 18 to pin 4 (MCLR*) of the SX. Plug the SX into an IC socket to protect its leads from repetitive plugging and unplugging from test circuits.

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Last updated January 27, 1999

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