IBM RS-232 manual Debugging

Inputs D0-D7 are pulled up via RN2 4.7K resistor network.

		U4
	74LS251		1 1							J 4
	4 D0	A		6	Q0	AD3		1 3
	3 D1	B	1 0	7	Q1	AD2		1 2		J 3
	2 D2	C	9	8	Q2	AD1		1 1		J 2
	1 D3	G	7	9	DatIn	AD0		1 0		J 1
	1 5 D4				[110C]
	1 4 D5			1	ASCII-OUT				RN1
	1 3 D6	W	6	1 8	STROBE				RN1
	1 2 D7	Y	5	CR1 1 1 5		BAUD		1 7
Data	Inputs			2 CR 3 1 6	RS-232			2	J 5
										+ 5
				R1					Open		Collector
				U1					RS-232 Output
										RS-232
								D1	R2	Ground
				U2
			Q1
									J 6		RS-232
									R3		Input
			R4	R5		V+	78L05		+ 5
			+ 5	+ 5					C1
					V+				+ 5

Care should be taken when interfacing to the inputs of this device. Remember, inputs are pulled high and are activated when they are connected to ground.

Debugging:

Basic checks: Verify all chips are located and oriented in the proper location. Also, check to make sure all pins are in the socket. Verify all parts are installed according to the directions and that you have a modem cable attached. Also verify there are no shorted solder connections on the 8SC board. We will also assume the 8SC board is oriented in the direction shown on the previous page.

Problem: Data is Not (or is Incorrectly) Received by the Computer:

Try: Make sure jumper J6 is installed between the left two posts. Make sure RS-232 lines are not reversed.

Make sure jumpers J1-J4 are set for the same address set in software. See "NCD-110C Addressing" for details. Make sure baud rate (J5) matches baud rate in your software.

Make sure the correct "COM" port is used in software. Make sure the RSB is properly connected and powered. Make sure resistor R1 is properly installed.

Make sure diode D1 is properly installed. Make sure Q1 is properly installed. Make sure 78L05 is properly installed.