The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 4
because of its longer write times. The program erases all of the stored programs and any
options selected with FPROG1-6 in U8.
Adding more NVRAM or EEPROM
If you want to add an additional 8K of NV RAM or EEPROM, wire another circuit exactly
like Figure 4-3’s, except connect pin 20 of the new NVRAM or EEPROM to A000h (pin
10 of U4) ORed with RESET, so that the chip will be accessed from A000h to BFFFh.
Adding EPROM
Adding EPROM requires more circuitry than NVRAM or EEPROM, because an EPROM
must have a programming voltage at its VPP pin during programming. To use the faster
FPROG commands, which follow Intel’s Intelligent programming algorithm, you should
also raise the EPROM’s supply voltage (VCC) to +6 volts during programming.
Although EPROMs do require additional components, once you have them in the circuit,
you can use the 8052-BASIC system as a general-purpose EPROM programmer, as
described in Chapter 13. You can store assembly-language programs or any information that
you want to save in EPROM, whether it’s for use by the 8052-BASIC system or another
project.
EPROM Types
Since EPROMs were first developed in the 1970’s, each generation of devices has allowed
larger capacities, faster programming, and reduced programming voltages. Although the
recommended programming algorithms, or procedures, for EPROMs are alike in many
ways, the details often vary, depending on the device and manufacturer.
Programming Algorithms
For critical applications, there is no substitute for consulting the EPROM’s data sheet and
following its recommendations exactly. But for general use, you can get reliable results with
most EPROMs by using one of the two algorithms supported by BASIC-52.
50-millisecond programming. This algorithm is an older, slower procedure. To program a
location in the EPROM, you apply a programming voltage to the VPP input, set the address
and data lines to the desired values, and apply a 50-millisecond programming pulse at the
PGM input to write the data into the EPROM at the selected address. You then increment the
address, apply the new data and programming pulse, and continue in this way until all
locations are programmed. After programming, you compare the EPROM’s contents to the
programming data to verify that all locations programmed correctly. (BASIC-52 varies from
this standard by verifying each location immediately after programming.)
56 The Microcontroller Idea Book