[N8VEM: 16418] z80 Buss buffering

[opticpow]

Hi All,

In down time between getting my boards build, I've been working on my
understanding of the hardware. I'm currently reading Build Your Own Z80
Computer by Ciarica, and have a question about the Address Bus and Output
Buffering (Page 98). The author discusses the reasons for buffering (which
makes sense) and I was wondering if the parts he describes (74367 for
Address Bus and 8212 for the data /control) are functionally what the
LS245's are doing on the SBCv2?

If that is the case, has my probing of the pins of the z80 on my SBC using
a scope & logic probe just been lucky not to overload the outputs on the
z80, or am I up the wrong tree?

Thanks,

Wayne.

[Borut]

Wayne,

You are correct, LS245 are used as address and data bus buffers in SBCv2.
No, you weren't just lucky. Scope probes are designed to have high
impedance, which basically means they
minimally load the circuit (about 10.000 times less than another ttl
circuit). That is why we usually use the
scope probes at 10x attenuation.
Logic probes usually use either an operational amplifier or a cmos circuit
and they fall in the same category.
At higher speeds capacitive loading becomes an issue, but n8vem sbcs aren't
there (yet :).

Borut

Post by opticpow
Hi All,
In down time between getting my boards build, I've been working on my
understanding of the hardware. I'm currently reading Build Your Own Z80
Computer by Ciarica, and have a question about the Address Bus and Output
Buffering (Page 98). The author discusses the reasons for buffering (which
makes sense) and I was wondering if the parts he describes (74367 for
Address Bus and 8212 for the data /control) are functionally what the
LS245's are doing on the SBCv2?
If that is the case, has my probing of the pins of the z80 on my SBC using
a scope & logic probe just been lucky not to overload the outputs on the
z80, or am I up the wrong tree?
Thanks,
Wayne.

[opticpow]

Thanks for the clarification Borut. I'm guessing the chips on the sbc that
are not on the other size of the buffers such as memory, uart 8255 etc.
together don't draw enough current to cause an issue with the z80?

Wayne.

Post by Borut
Wayne,
You are correct, LS245 are used as address and data bus buffers in SBCv2.
No, you weren't just lucky. Scope probes are designed to have high
impedance, which basically means they
minimally load the circuit (about 10.000 times less than another ttl
circuit). That is why we usually use the
scope probes at 10x attenuation.
Logic probes usually use either an operational amplifier or a cmos circuit
and they fall in the same category.
At higher speeds capacitive loading becomes an issue, but n8vem sbcs
aren't there (yet :).
Borut

Post by opticpow
Hi All,
In down time between getting my boards build, I've been working on my
understanding of the hardware. I'm currently reading Build Your Own Z80
Computer by Ciarica, and have a question about the Address Bus and Output
Buffering (Page 98). The author discusses the reasons for buffering (which
makes sense) and I was wondering if the parts he describes (74367 for
Address Bus and 8212 for the data /control) are functionally what the
LS245's are doing on the SBCv2?
If that is the case, has my probing of the pins of the z80 on my SBC
using a scope & logic probe just been lucky not to overload the outputs on
the z80, or am I up the wrong tree?
Thanks,
Wayne.

[Andrew Lynch]

Hi! There is a version of the BYOZC on scribd in case anyone wants to
follow along.



Steve released the book into the public domain just because he is just a
great guy.


Thanks and have a nice day!

Andrew lYnch



From: n8vem-/***@public.gmane.org [mailto:n8vem-/***@public.gmane.org] On Behalf Of
opticpow
Sent: Tuesday, October 29, 2013 1:21 AM
To: n8vem-/***@public.gmane.org
Subject: [N8VEM: 16418] z80 Buss buffering



Hi All,

In down time between getting my boards build, I've been working on my
understanding of the hardware. I'm currently reading Build Your Own Z80
Computer by Ciarica, and have a question about the Address Bus and Output
Buffering (Page 98). The author discusses the reasons for buffering (which
makes sense) and I was wondering if the parts he describes (74367 for
Address Bus and 8212 for the data /control) are functionally what the
LS245's are doing on the SBCv2?

If that is the case, has my probing of the pins of the z80 on my SBC using a
scope & logic probe just been lucky not to overload the outputs on the z80,
or am I up the wrong tree?

Thanks,

Wayne.
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[opticpow]

Thanks Andrew, should of though about providing a link!
http://www.scribd.com/doc/13388965/build-your-own-z80-computer