In this lab you will recover a message I stored in an EPROM chip. EPROM stands for Erasable Programmable Read Only Memory. EPROM's are a special type of ROM. ROM's store information. This information is retrieved by selecting a particular segment of the chip using its address. The information then becomes available in digital form on the output pins of the chip.
As the name EPROM suggests these chips can be erased and reused. The erasing process involves exposing the chips to intense UV light. MSOE has an EPROM eraser. EPROM chips can also be programmed and erased by the user (as opposed to ROM chips that must be programmed by the manufacturer and PROM chips that can only be programmed once). MSOE has several EPROM programmers available for student use. These devices connect to the serial outputs (COM ports) of any MS-DOS based PC. They come with software that includes options for help, to check if the chip has be erased, to program the chip using a hex file and to program the chip using a binary or ASCII file. You will not need to program any chips for this lab, but may want to use the programmers later in this course or in some other course.
There are at least three types of TTL output circuits. As an optional part of this experiment, you may investigate the electrical behavior of these circuits.
Work with a new partner this week. Be sure to record your work in your lab notebook.
| 1 | 2716 (2K x 8) EPROM chip with prepared ASCII message (provided by the instructor) |
| 2 | 9370 Hex display card (optional) |
| 2 | 7493 4-bit binary counter (optional) |
| 1 | 74LS157 Quad 2-to-1 multiplexer (optional) |
| 1 | Digi-Designer with wires |
| 1 | Logic probe (optional, for debugging) |
| 1 | Tackle Box (optional, for part II) |
| Other TTL chips (optional, for part II) |
Part Ia: Use the equipment and data sheets provided to recover an ASCII message from your EPROM chip.
Part Ib: Use the equipment and data sheets provided to recover the Truth Table for Q0 as a function of A3, A2, A1 and A0 from your EPROM chip.
The chip you will be using, a 2716, has 11 address pins and 8 output pins (1 byte). The message is stored 7-bit ASCII code in the first 16 bytes (addresses 00002 through 11112) on the chip. See Table 1-5 on page 23 in your text for a listing of the 7-bit ASCII codes and pages 180 to 186 for a discussion of ROM's.
You will need to read 8 bits of output data from your EPROM. You may use the 4 LED's on the Digi-Designer to read this data 4 bits (one nibble) at a time. Using the LED's you could read the low order nibble, rewire your circuit and then read the high order nibble. Another option would be to multiplex the outputs to the LED's using the 74LS157 chip. You could switch between the low and high order nibbles electrically with this approach. The Hex display cards can display 4-bit binary numbers in hexadecimal format. You could use the Hex display cards for the most sophisticated form of output.
You will need to address at least the first 16 bytes of memory on your ROM chip. This will require 4 address bits. Some of the messages are more that 16 bytes long, but you are only required to read the first 16 bytes. You may want to allow for 5 address bits to see the complete message. You can use the 4 switches on the Digi-Designer to generate the 4-bit addresses. Another option is to use one or two (for 5 or more address bits) binary counters triggered by the Digi-Designer clock or push buttons. Remember to tie all unused address inputs low, otherwise they'll drift high and you wont be able to access the message stored in your chip.
Review pages 412 to 422 in your textbook.
Get at least one chip with each of the following types of TTL outputs: open collector, totem-pole (the standard type) and 3-state outputs. Confirm that these chips act as you expect them to.
One way to investigate the electrical behavior of the outputs is to develop Thevenin equivalent circuits for them. If you do this, be sure to use resistors between the outputs and Vcc and ground to keep all currents within the limits specified by the manufacturers. You should not need to limit currents to and from the 3-state outputs when they are in the high impedance state.