Memory is an essential component of any microprocessor-based system. the memory stores the data and instructions for the microprocessor. these are different types of memories. The Read/Write memory is made of registers and each register has a group of flip-flops. the flip-flops are named memory cells. the number of bits stored in a register is called a memory word. whereas ROM stores information permanently and can not be altered.
The capacity of a memory chip is generally measured in terms of the number of bits or bytes its stores. as most chips contain more than a few thousand bits, the memory capacity is expressed in kilobits (KB) or megabits (MB). here b denotes the bits, not bytes. the capacity of a memory chip can be calculated by multiplying the number of memory words by the number of bits per word.
Each word inside a chip has a unique address. For example, the HM 6264 static RAM has a total of 8096 (8K) words. the word addresses range from 0 to 8095. each word of this memory chip consists of 8-bits. thus the capacity of this memory chip is 8K x 8 bits or 64 kb. the below-given table shows memory chips with their organizations.
Memory chips with their Organization
|HM6116||Hitachi||Static RAM||2 K x 8|
|HM 6264||Hitachi||Static RAM||8 K x 8|
|HM 6287||Hitachi||Static RAM||64 K x 1|
|TMM 41256||Toshiba||Dynamic RAM||256 K x 1|
|TC 514256||Toshiba||Dynamic RAM||256 K x 4|
|TC 51100||Toshiba||Dynamic RAM||1M x 1|
|TC 571000||Toshiba||EPROM||128 K x 8|
|TCS 534000||Toshiba||Mash ROM||512 K x 8|
A memory system may consist of several chips. which chips are selected by the designer depending on several factors. the total memory capacity and the word size are two of the factors, which are governing the chip selection. for example, to have a 16K word memory system with an 8-bit word size, a designer may use two HM 6264 (8K x 8) memory chips.
Any memory chip can be compared to a book, with the lower two Hex digits considered as the line number and the higher digits considered as the page number. i.e -00H to FFH form a page. there are a total of 256 lines on a page.
Four pages constitute 1K memory, i.e. the address starting from 0000H to 03FFH is 1K memory. this is represented in the below-given figure (a). also the below figure (b) shows a 2K memory (for example memory chip HM 6116).
- Demultiplexing of address/data bus
- Pin configuration of 8085 microprocessor
- Basic operations of Microprocessor
- 8085 microprocessor architecture