25 Jun
2005
25 Jun
'05
4:49 p.m.
> What programmer can I look for that has the
ability to program a
> 2708?
I have a Softy 2 that can do it if you're really stuck.
Not just that, the programming algorithm is different
to most
other EPROMs. IIRC you have to program all locations in sequence,
giving each one a 1ms (IIRC) programming pulse, and repeat that
50 times.
Any bit in any byte can be individually programmed from 1 to 0.
There are no sequence requirements, the programming pulse is one
pulse of 50ms per location programmed.
You can't program odd locations like you can in
later EPROMs.
You can, it's EPROM microcontrollers like the 68705 that need to
be programmed in sequence.
Lee.
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25 Jun
25 Jun
5:42 p.m.
From: "lee davison" <leeedavison at yahoo.co.uk>
Sent: Saturday, June 25, 2005 6:49 PM
The 2708 can be programmed non-sequentially and the pulse can either be one
50ms or multiple shorter pulses that adds up to 50ms. There are other
"fast" techniques where you write with a short pulse, read and rewrite until
all cells verify then run one more short pulse write.
Randy
www.s100-manuals.com
> What
programmer can I look for that has the ability to program a
> 2708?
I have a Softy 2 that can do it if you're really stuck.
Not just that, the programming algorithm is
different to most
other EPROMs. IIRC you have to program all locations in sequence,
giving each one a 1ms (IIRC) programming pulse, and repeat that
50 times.
Any bit in any byte can be individually programmed from 1 to 0.
There are no sequence requirements, the programming pulse is one
pulse of 50ms per location programmed.
You can't program odd locations like you can
in later EPROMs.
You can, it's EPROM microcontrollers like the 68705 that need to
be programmed in sequence.
Lee. 
26 Jun
26 Jun
3:26 p.m.
Not just that,
the programming algorithm is different to most
other EPROMs. IIRC you have to program all locations in sequence,
giving each one a 1ms (IIRC) programming pulse, and repeat that
50 times.
Any bit in any byte can be individually programmed from 1 to 0.
There are no sequence requirements, the programming pulse is one
pulse of 50ms per location programmed. You can't
program odd locations like you can in later EPROMs.
You can, it's EPROM microcontrollers like the 68705 that need to
be programmed in sequence.
7:01 p.m.
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
Sent: Sunday, June 26, 2005 5:26 PM
Well, I'll admit that I was working from memory last night, but I've just
checked the Intel 1977 Data Catalog :
Under '2708/2704 family programming it says :
'The circuit is set up for programming operation by raising the CS/WE
input (pin 20) to +12V. The word address is selected in the same manner
as in read mode. Data to be programmed are presented, 8 bits in parallel,
to the data output lines (O1--O8). Logic Levels for address and data
lines and the supply voltages are the same as for the read mode. After
address and data set up, one program pulse per address is applied to the
program input (pin 18). One pass through all addresses is defined as a
rpgoram loop. The number of loops (N) requirded is a function of the
program pulse width (t_PW) addording to N * t_PW >= 100ms.
The width of the program pulse is from 0.1 to 1 ms. The number of loops
(N) is from a minimum of 100 (t_PW = 1ms) to greater than 1000 (t_PW =
0.1ms). There must be N successive loops through all 1024 addresses. It
is not pwemitted to apply N program pulses to an address and then chenage
to the next address to be programmed.
...'
Maybe other manufactures had simpler algorithms for their 2708s, but the
Intel data book makes it very clear you do have to program all locations.
(It gives examples where only some locations are to be changed. The
unchanged ones have to be reprogrammed with their existing contents, you
can't skip over them.
-tony
Intel changed the specifications of the 2708 a couple of times, later docs
state it does not require programming from address 0.
I have changed individual bits (only from a high to low, to go from low to
high the entire chip must be erased).
The later docs still state sequential writing but no longer require starting
at 0 but I have written non sequentially and can swear by that. I wrote a
program that verified before writing to speed up programming, this skipped
many bytes and I used it to modify previously written EPROM's. The buffer
in RAM was sequentially read but the writing was NOT sequential it would
skip bytes when a write was not needed.
Any byte can have high bits changed to low even if they were previously
programmed.
Randy
www.s100-manuals.com
Not just that, the programming algorithm is different
to most
other EPROMs. IIRC you have to program all locations in sequence,
giving each one a 1ms (IIRC) programming pulse, and repeat that
50 times.
Any bit in any byte can be individually programmed from 1 to 0.
There are no sequence requirements, the programming pulse is one
pulse of 50ms per location programmed. You
can't program odd locations like you can in later EPROMs.
You can, it's EPROM microcontrollers like the 68705 that need to
be programmed in sequence.
27 Jun
27 Jun
2:49 p.m.
Intel changed the specifications of the 2708 a couple
of times, later docs
state it does not require programming from address 0.
But did they also change the design of the chip, I wonder. Later 2708s
may be more forgiving as to the programming algorithm they'll accept.
Since Intel were so definite about having to go through all locations in
order n times in the data sheet I have, I would certainly want to do it
that way. Other methods might well damage the chip or lead to poor data
retention.
I have changed individual bits (only from a high to low, to go from low to
high the entire chip must be erased).
You can change individual bits, sure. The data sheet tells you how to do
that.
You have to go through _all_ the locations. If a locations is to be
unchanged, you program it again with its current contents (a special case
of this is that if you want to leave a location totally unprogrammed
after erasing the chip, you re-write it with 0xFF).
The later docs still state sequential writing but no longer require starting
at 0 but I have written non sequentially and can swear by that. I wrote a
program that verified before writing to speed up programming, this skipped
Oh, it probably worked. But I wouldn't recomend doing it. 2708s are
getting harder to find, so I'd not want to risk damaging one. And I
certainly don't want to have to trace a fault caused by an unreliable bit
in an EPROM. I would follow the manfacturer's instructions...
It reminds me af a friend who programmed 27128s with a single 1ms pulse
per location. It seemed to work. They verified OK. And then a bit later
on he got data-rot....
-tony
28 Jun
28 Jun
4:53 p.m.
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
Sent: Monday, June 27, 2005 4:49 PM
to
starting
> Intel changed the specifications of the 2708 a
couple of times, later
docs
state it does
not require programming from address 0.
But did they also change the design of the chip, I wonder. Later 2708s
may be more forgiving as to the programming algorithm they'll accept.
Since Intel were so definite about having to go through all locations in
order n times in the data sheet I have, I would certainly want to do it
that way. Other methods might well damage the chip or lead to poor data
retention.
>
> I have changed individual bits (only from a high to low, to go from low high the
entire chip must be erased).
You can change individual bits, sure. The data sheet tells you how to do
that.
You have to go through _all_ the locations. If a locations is to be
unchanged, you program it again with its current contents (a special case
of this is that if you want to leave a location totally unprogrammed
after erasing the chip, you re-write it with 0xFF).
>
> The later docs still state sequential writing but no longer require > at 0 but I have written non sequentially and can
swear by that. I wrote
a
> program that verified before writing to speed up
programming, this
skipped
Oh, it probably worked. But I wouldn't recomend doing it. 2708s are
getting harder to find, so I'd not want to risk damaging one. And I
certainly don't want to have to trace a fault caused by an unreliable bit
in an EPROM. I would follow the manfacturer's instructions...
It reminds me af a friend who programmed 27128s with a single 1ms pulse
per location. It seemed to work. They verified OK. And then a bit later
on he got data-rot....
-tony
As I stated you can not rely on a single read to verify the data is
recorded, once you get a verify you MUST give it another write cycle to
ensure data.
For the later docs for the 27128's it confirms this and adds that VCC should
be raised to 6v.
Randy
www.s100-manuals.com
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