As a result, we receive many inquiries regarding memory chips and are continually forced to see that there is still a great need for information in this area. As a result, we are now distributing here the basic information for programming memory chips, such as eproms/eeproms and Flash chips. Our discussion will focus on the different types of memory chips, comparing what the 27C, 28C, or 29F series can and cannot do.
How do memory chips work?
There are two types of memory chips programmers: program memory and data memory. In this context, a program is a series of instructions (command string) for a microprocessor (= computing unit). Data could consist of temperature measurements taken by a temperature measurement system, for example, or any other type of data.
A series of numbers – zeros and ones (=bits) is stored on the memory chip programer / data. Either a 0 or a 1 can be a Bit. Having a comprehensive overview of these Bits can be difficult; therefore, they are grouped into groups. Eight bits are a “Byte”, 16 bits are a “Word” and four bits are a “Nibble”.
Bytes were also called Kilo and Mega due to the binary nature (zero or one) of the digital systems. Kilo means 1024 (2 to the 10th power) and Mega means 1024 * 1024 = 1048576. Therefore, 1024 bytes make up a Kilobyte and 10485776 bytes make up a Megabyte.
An organization of a memory chip
Memory chips with 8 bits (the most common type) store bits in Bytes (8 bits) that are referred to as “addresses”. A Byte can be accessed at this address, and the eight bits of the accessed address are output on the eight data ports. An 8-megabit chip like the 27c801 contains 1048576 bytes (= 8388608 bits). Every Byte has its own address, numbered from 00000h through FFFFFh (corresponding to 0 to 1048575).
As well as 8 Bit memory chips, there are 16 Bit memory chips, serial 1-Bit memory chips, and (rarely/old) 4 Bit memory chips.
(27/27C…) EPROM memory chips
EPROM is an Erasable Programmable Read Only Memory. Can you explain in more detail what it means?
“Erasable” refers to the ability to remove the data from it. A 254 nm wavelength is used to eradicate these chips by exposing them to intense ultraviolet light. We deal with erasing eproms with UV-C light in further detail below.
“Programmable” means that a program or data can be programmed (burned) into this chip. For programming, a programming device such as the Batronix Eprommer or the Galep-4 is required.
“Read Only Memory” means that this type of memory can be read out but not programmed in the target device.
This memory type can be burned (programmed) by a programming device and then retains its data until an erasing device erases it. During the programming process, any desired number of bits from one to zero can be programmed. Eproms can also be programmed repeatedly without being erased as long as the bits are only changed from one to zero or remain on zero. To change a bit from zero to one, erasure is necessary.
Since the quartz glass window required for erasing the chip with UV-C light is a big part of the production costs for the chip, this chip is available with and without this window. Without the window, the chip cannot be erased using UV-C light. The eproms with windows are also called UV eproms; the ones without are called OTP (=One Time Programmable) eproms.
EEPROM memory chips (28C…)
The name EEPROM stands for Electrically Erasable Programmable Read Only Memory. These are constructed like EPROMS, but allow the erasing of individual bytes or the entire memory space electrically without UV light. Since individual bytes can be erased without erasing everything, these individual bytes can be overwritten, in effect. However, with an EEPROM, the burning process clearly takes longer than with an EPROM – up to several milliseconds per byte. To make up this disadvantage, EEPROMS like AT28C256’s were equipped with a function for the programming of so-called blocks. In this process, 64, 128 or 256 bytes at once are loaded into the memory chip and programmed simultaneously as a block. This clearly shortens programming times.
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