8051 question

[Spehro Pefhany]

Oh...i like *analog* transistors better...

The term "digital transistor" refers to transistors with series base
and sometimes parallel E-B resistors on the same chip. Obviously, they
are intended (and spec'd) for switching applications. You're free,
however, to use them for analog applications. I think the term came
from our Japanese friends..

http://www.rohm.com/products/databook/tr/pdf/dtc144ee.pdf



Best regards,
Spehro Pefhany

 

[Eeyore]

The term "digital transistor" refers to transistors with series base
and sometimes parallel E-B resistors on the same chip. Obviously, they
are intended (and spec'd) for switching applications. You're free,
however, to use them for analog applications. I think the term came
from our Japanese friends..

http://www.rohm.com/products/databook/tr/pdf/dtc144ee.pdf

Very handy wee beasties. I used 32 per board DTA114 IIRC that drove a VFD (from an
8051 as it happens).

Graham

 

[mpm]

That is why I had to place an unused variable in my code at address 0.
Solved the problem.

But creates another problem.
Now you can't jump past the INTO interrupt vector off-page. (located
at 0003H)
You'll have to tell the Assembler / Compiler to do an in-page jump to
avoid servicing the interrupt.

No big deal, I guess.

-mpm

 

[Henry Kiefer]

But creates another problem.
Now you can't jump past the INTO interrupt vector off-page. (located
at 0003H)
You'll have to tell the Assembler / Compiler to do an in-page jump to
avoid servicing the interrupt.

No big deal, I guess.

Typically you don't have RAM at bottom of memory. So there is no
problem! But the ' Intel feature' repeats on every memory chip in the
system!

We had an EEPROM at 8000h in XDATA space. Sometimes the first byte of
this EEPROM was overwritten. It depends on ramp-up speed of VCC and Q
(=delay) of the oscillator.
Some memoriy devices restrict the write access in some way - mostly on
VCC value. As long as the memory device blocks the write all is ok.
Thereafter it depends...

To be save: Don't use the first byte of EVERY writable memory in the system.

A small risk scenario persists for corruption of another byte address
somewhere. Do you know when which output line in the controller goes
active??

At least for us the problem was completely solved.

Or go the WR-blocking way with for example a MAX691.


- Henry

 

[Robert Baer]

The term "digital transistor" refers to transistors with series base
and sometimes parallel E-B resistors on the same chip. Obviously, they
are intended (and spec'd) for switching applications. You're free,
however, to use them for analog applications. I think the term came
from our Japanese friends..

http://www.rohm.com/products/databook/tr/pdf/dtc144ee.pdf



Best regards,
Spehro Pefhany

I know; just could not "resist" the 'omely pun.

 

[Robert Baer]

But creates another problem.
Now you can't jump past the INTO interrupt vector off-page. (located
at 0003H)
You'll have to tell the Assembler / Compiler to do an in-page jump to
avoid servicing the interrupt.

No big deal, I guess.

-mpm

Been ages since i wrote code for the 8051s, but wouldn't a NOP there
help?

 

[MooseFET]

But creates another problem.
Now you can't jump past the INTO interrupt vector off-page. (located
at 0003H)
You'll have to tell the Assembler / Compiler to do an in-page jump to
avoid servicing the interrupt.

Since the code and memory spaces are not the same, you don't really
have this conflict. The 64K Xdata space gets written to but there is
no write for the PSEN enabled code space.

You can condition the address decoder for the RAMs with the RESET line
to block the access during the reset time.

 

[MooseFET]

Interesting. How do you do that ?

I usually use an HC or HCT decoder chip or something like that to do
the address decode. All you really need to do is have an input on the
decoder that must be low for the CE/ of the RAM to be taken low. A
simple RC with the capacitor to the VCC prevents unwanted chip selects
and hence unwanted writes.