Digital Circuits for High School Students (Part 3)

Prepared by Charles S. Tritt, Ph.D.
July 18, 1997

Equipment (for each pair of students working together)

1   Digi Designer

1   Set of wires (these should come with the Digi Designer)

1   27x32 32K (4K x 8) EPROM chip

Introduction

Memory makes up a very important part of digital computers. One type of memory is Erasable, Programmable Read Only Memory (EPROM). You will retrieve an ASCII message stored in an 2732 EPROM chip in this exercise.

Safety Considerations

Dangerous line voltages are present at the outlets on your work bench. Do not inert anything other than approved power plugs into these outlets.

The voltages and currents produced by the Digi Designer are generally safe. However, you should not short +5V (Vcc) or logic High outputs directly to ground or intentionally make yourself part of a logic circuit.

Chip pins and the tips of the small wires may be sharp. Handle with care. Chips can become very hot if wired incorrectly. Be careful.

Procedures

ASCII Codes and EPROM's

Figure 1 -- Pin outs for the 2732 EPROM chip.

Insert your 2732 into the bread board on your Digi Designer. Connect power and ground to pins 24 and 12, respectively. Make the following connections from left to right across the lower edge of the chip:

Pin	Function	Connection
1	A7 input	Ground, logic Zero
2	A6 input	Ground, logic Zero
3	A5 input	Ground, logic Zero
4	A4 input	Ground, logic Zero
5	A3 input	J15, switch
6	A2 input	J16, switch
7	A1 input	J17, switch
8	A0 input	J18, switch
9	O0 output	J4, lamp monitor
10	O1 output	J3, lamp monitor
11	O2 output	J2, lamp monitor

Make the following connections from right to left across the upper edge of the chip:

Ground, logic Zero

Pin	Function	Connection
13	O3 output	J1, lamp monitor
14	O4 output	No connection
15	O5 output	No connection
16	O6 output	No connection
17	O7 output	No connection
18	CE' input	Ground, logic Zero
19	A10 input	Ground, logic Zero
20	OE'/Vpp input
21	A11 input	Ground, logic Zero
22	A9 input	Ground, logic Zero
23	A8 input	Ground, logic Zero

Enter all 16 possible address values for A (i.e., all possible combinations of A₀ through A₃) and complete the right hand (low order) columns of the table in your work sheet. Then, change the following wires.

Connects with	Move from	Move to
Lamp monitor J4	Pin 9 (O0)	Pin 14 (O4)
Lamp monitor J3	Pin 10 (O1)	Pin 15 (O5)
Lamp monitor J2	Pin 11 (O2)	Pin 16 (O6)
Lamp monitor J1	Pin 13 (O3)	Pin 17 (O7)

Again enter all 16 possible address values for A (i.e., all possible combinations of A₀ through A₃) and complete the left hand (high order) columns of the table in your work sheet. Finally, translate your codes first into Hex values and then ASCII characters and write your message on the chalk board using the following tables.

Hex Values

Binary	Hex		Binary	Hex
0000	0		1000	8
0001	1		1001	9
0010	2		1010	A
0011	3		1011	B
0100	4		1100	C
0101	5		1101	D
0110	6		1110	E
0111	7		1111	F

ASCII Codes

		Hex1	0	1	2	3	4	5	6	7
		b6b5b4	000	001	010	011	100	101	110	111
Hex0	b3b2b1b0
0	0000		NUL	DLE	SP	0	@	P	`	p
1	0001		SOH	DCI	!	1	A	Q	a	q
2	0010		STX	DC2	"	2	B	R	b	r
3	0011		ETX	DC3	#	3	C	S	c	s
4	0100		EOT	DC4	$	4	D	T	d	t
5	0101		ENQ	NAK	%	5	E	U	e	u
6	0110		ACK	SYN	&	6	F	V	f	v
7	0111		BEL	ETB	'	7	G	W	g	w
8	1000		BS	CAN	(	8	H	X	h	x
9	1001		HT	EM	)	9	I	Y	i	y
A	1010		LF	SUB	*	:	J	Z	j	z
B	1011		VT	ESC	+	;	K	[	k	{
C	1100		FF	FS	,	<	L	\	l	|
D	1101		CR	GS	_	=	M	]	m	}
E	1110		SO	RS	.	>	N	^	n	~
F	1111		SI	US	/	?	O	-	o	DEL

ASCII codes less that 20₁₆ are special hardware control characters. The only ones of these you are likely to find stored in your chip are line feed, LF, and carriage return, CR.

The chip pin out diagram in this document was taken from Fairchild/National Instruments chip data sheet.