The pin details are given below: V cc, GND = +5V and Ground A 11 -A 0 = address lines. Fig.2.19 Intel 2716 Read Only Memory

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1 Lecture-8 Typical Memory Chips: In previous lecture, the different types of static memories were discussed. All these memories are random access memories. Any memory location can be accessed in a random fashion without regard to another location. The access time is same for each memory locations. Memory chip may be volatile or non-volatile depending on whether it is RWM or ROM. Some of the basic memory chips are discussed below: INTEL 2716 EPROM: This is an Ultra Violet Erasable Programmable Read Only Memory (UVEPROM). Intel 2716 has 16k bits (2k x 8= 16,384) or 2048 bytes of memory. It has 11 address lines A 10 A 9..A 1 A 0 and 8 data lines D 7..D 0. The pin connection & logic symbolism is shown in fig. (a) and (b) respectively. Figure (a) Figure (b) Fig.2.19 Intel 2716 Read Only Memory The pin details are given below: V cc, GND = +5V and Ground A 11 -A 0 = address lines

2 D 7 -D 0 = data lines V pp = Programming voltage pin OE = output enable pin to enable the output data buffer. CE/PROG= It is a dual function pin. While programming V pp pin must be held at 25 volts. It this chip is used in a microcomputer after programming this pin must be held at +5V. This is an erasable PROM. The stored data can be erased by exposing the window in the PROM to ultra violet light. Data may be erased when continuously exposed in fluorescent light or sunlight. When the EPROM is completely erased then each bit of the memory must be 1. If one wants to make it 0, 0 should be written there. Although, only 0s will be programmed, both 1s and 0s will be present in the data word. Therefore, before programming each memory location stores FF H and desired data can be stored by selectively programming 0s into the designated bit locations. To store any data at the addressed location a 50ms active programming pulse is applied at PROG. To program 2716, the following procedures are used; i) Apply 25 V DC to pin no. 21(V pp ). ii) Set the OE HIGH (+5V). iii) Set up the address of the memory location to be programmed at the address bus, iv) Set up the 8-bit data to be programmed on the data bus, v) Apply a 50 msec positive TTL pulse to the CE/PROG input.

3 The above procedure is repeated until all desired locations have been programmed. One can program any location at any time, either individually, sequentially or at random. The program pulse has maximum width of 55 msec. The chip 2716 must not be programmed with a DC signal applied to CE/PROG. Instead a pulse of 50 msec shall be applied. All the above actions are carried out in a separate unit called PROM programmer. It requires only 100 sec to program all the 2048 memory locations. The circuit connection for programming 2716 is shown below: Fig.2.20 Intel 2716 Erasable Programmable Read Only Memory The waveforms during programming are shown in figure below:

4 Once the programme is written down in memory chip, it cannot be erased. If we want to change it we put it in UV eraser and erase it and then programme it again. Once the chip is programmed, it can be used to read data again and again. When the two inputs CE and OE are in their normal state (HIGH) the output is tri-stated. Now one can only perform a MEMORY READ operation from this device. The following is the procedure for a MEMORY READ operation. i) Set up the address of the memory location to be used on the address bus. ii) Set up the CE signal active (LOW). iii) OE pin is made low for short duration to enable the output. In a processor based system, RD control signal of the processor is connected to OE terminal. The connection diagram for MEMORY READ operation is shown in figure:

5 The waveforms during read operation are shown in figure below: The waveforms for the chip show that the data outputs became valid after a delay for setting up the addresses t ACC or enable the chip or enabling the output whichever is completed last.

6 INTEL 6116 RAM: It is a 2k x 8 static Read Write Memory (RWM). The pin connection is shown in fig.(a) and the logic symbol is shown in fig.(b). Fig (a)

7 Fig (b) The truth table for control signals is as follows: CE WE OE Operation REMARKS 0 0 X WRITE The data available on the data bus shall be written on the addressed location. The original contents are lost. The new labes it place READ The content of the addressed location is READ on to the output data line The content other addressed location is not destroyed No operation Output is Tri state. 1 X X No operation Output is Tri state.

8 The two chips Intel 2716 and Intel 6116 are pin by pin compatible and can be used in place of other. The pin by pin compatibility of 6116 with 2716 has an advantage. In the initial stage of a programme development Intel 6116 is put in the 24 pin socket provided on the microcomputer and the programme is developed. Once the programme is completely tested and satisfactory then using a PROM programmer the programme can be transferred to 2716 ROM for permanent storage. Thereafter, 2716 can be put directly to the same socket occupied by A simple jumper should be provided for pin no 21. This is shown in figure below.

Lecture-7 Characteristics of Memory: In the broad sense, a microcomputer memory system can be logically divided into three groups: 1) Processor

Lecture-7 Characteristics of Memory: In the broad sense, a microcomputer memory system can be logically divided into three groups: 1) Processor memory 2) Primary or main memory 3) Secondary memory Processor