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docs/_docs/prom-500-pd27.md
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@ -18,7 +18,7 @@ Chips that use high voltage pulses for each byte are not supported. For those c
|:--- |:--- |:--- |:--- |:--- | |:--- |:--- |:--- |:--- |:--- |
|[M27256](#m27256) |ST Micro |EPROM |27 |VCC=6V, VPP=12.5V to pgm| |[M27256](#m27256) |ST Micro |EPROM |27 |VCC=6V, VPP=12.5V to pgm|
|[M27C256](#m27c256) |ST Micro |EPROM |27 |VCC=6.5V, VPP=12.75V to pgm| |[M27C256](#m27c256) |ST Micro |EPROM |27 |VCC=6.5V, VPP=12.75V to pgm|
|[W27C257](#w27c257,-27e257,-27c512) |Winbond |EEPROM |27 |Continuous 12V or 14V for program/erase| |[W27C257](#w27c257-27e257-27c512) |Winbond |EEPROM |27 |Continuous 12V or 14V for program/erase|
|[SST27SF020](#sst27sf020)|SST |Flash |27 |12V continuous for pgm/erase| |[SST27SF020](#sst27sf020)|SST |Flash |27 |12V continuous for pgm/erase|
@ -46,7 +46,7 @@ The Winbond W27C257 and W27E257 appear to be identical 32Kx8 EEPROMs. The 27C v
The 257 EEPROMs have a _VPP_ pin that needs a constant 12V during programming. Unlike the newer 28C EEPROMs, these chips do not automatically erase before writing to a location. Instead, the entire chip is erased by applying 14V to _VPP_ and _A9_ and then pulsing _CE_. To erase the chip, assert the voltages on _VPP_ and _A9_ and then issue the _Erase_ command from the terminal. The 257 EEPROMs have a _VPP_ pin that needs a constant 12V during programming. Unlike the newer 28C EEPROMs, these chips do not automatically erase before writing to a location. Instead, the entire chip is erased by applying 14V to _VPP_ and _A9_ and then pulsing _CE_. To erase the chip, assert the voltages on _VPP_ and _A9_ and then issue the _Erase_ command from the terminal.
Unlike the 257 chips, the W27C512 does not have a dedicated pin for the programming voltage and instead uses the 12V on _OE_ pin to place the chip in programming mode. The verify operation requires that the _OE_ pin be switched to _LOW_ and there is no hardware support for this, so the current code supports the 512 chip by doing a single write cycle with no verify. Unlike the 257 chips, the W27C512 does not have a dedicated pin for the programming voltage and instead uses 12V on the _OE_ pin to place the chip in programming mode. The verify operation requires that the _OE_ pin be switched to _LOW_ and there is no hardware support for this, so the current code supports the 512 chip by doing a single write cycle with no verify.
Because the chips use a constant high voltage for programming instead of a pulse, an external power supply and two diodes can be used to supply either 5V or 12V to the pins for programming and erasing. Because the chips use a constant high voltage for programming instead of a pulse, an external power supply and two diodes can be used to supply either 5V or 12V to the pins for programming and erasing.
@ -54,15 +54,9 @@ Note that the W27x257 chip are almost a drop-in replacement for the 28C256. The
## SST27SF020 ## SST27SF020
The Silicon Storage SST27SF0x0 are programmed similarly to the 27C257 in that a constant The Silicon Storage SST27SF0x0 are programmed similarly to the 27C257 in that a constant voltage is applied for program and erase operations. Unlike the 27C257, these have a dedicated WE pin that controls programming and erasing. Another difference is that they do not have a verify operation to read back the programmed data.
voltage is applied for program and erase operations. Unlike the 27C257, these have a
dedicated WE pin that controls programming and erasing. Another difference is that they
do not have a verify operation to read back the programmed data.
These Flash chips have a _VPP_ pin that needs a constant 12V during programming. Unlike These Flash chips have a _VPP_ pin that needs a constant 12V during programming. Unlike the newer 28C EEPROMs, these chips do not automatically erase before writing to a location. Instead, the entire chip is erased by applying 12V to _VPP_ and _A9_ and then pulsing _WE_.
the newer 28C EEPROMs, these chips do not automatically erase before writing to a
location. Instead, the entire chip is erased by applying 12V to _VPP_ and _A9_ and then
pulsing _WE_.
## Chips to be Tested ## Chips to be Tested