Hi, these days I found a PModCLP I purchased some years ago and decided to reimplement the control for it.
In particular, I decided to operate the module in a differnt manner:
use the 4 bit mode to spare some lines
read status bit to know when a command has been finished
As a consequence, there is bidirectional data transfer on the data bus including High-Z phases and DB0 to DB3 will be left unconnected on the hardware.
When measuring DB7 to see the status, I got quite surprised because I measured up to 4.8V on the data line - far beyond the PMod specs! When looking at the schematics (RevB), I see this VTerm2.5 stuff which I guess should limit the voltage on the 3.3V inputs. But I don't understand how this can work: as soon as an open DB pin exceeds 2.5V + 0.7V = 3.2V current will flow back to IC1, increasing voltage at that output. The regulator will shut down and the whole VTerm potential will mount, affecting also the other outputs. Actually I measure 4.6 at C1 when grounding DB0 to DB3, a bit more when leaving all DBs open.
As I understand it, this circuit will only protect outputs but not inputs. Am I right or do I miss someting?
BTW, measuring the current to ground on a DB pin gives me about 2.5mA, and a total of 18mA for all 8 pins. This is too high compared to what the KS0066U datasheet states. Does anybody have other measurements?
Question
juergenR
Hi, these days I found a PModCLP I purchased some years ago and decided to reimplement the control for it.
In particular, I decided to operate the module in a differnt manner:
As a consequence, there is bidirectional data transfer on the data bus including High-Z phases and DB0 to DB3 will be left unconnected on the hardware.
When measuring DB7 to see the status, I got quite surprised because I measured up to 4.8V on the data line - far beyond the PMod specs! When looking at the schematics (RevB), I see this VTerm2.5 stuff which I guess should limit the voltage on the 3.3V inputs. But I don't understand how this can work: as soon as an open DB pin exceeds 2.5V + 0.7V = 3.2V current will flow back to IC1, increasing voltage at that output. The regulator will shut down and the whole VTerm potential will mount, affecting also the other outputs. Actually I measure 4.6 at C1 when grounding DB0 to DB3, a bit more when leaving all DBs open.
As I understand it, this circuit will only protect outputs but not inputs. Am I right or do I miss someting?
BTW, measuring the current to ground on a DB pin gives me about 2.5mA, and a total of 18mA for all 8 pins. This is too high compared to what the KS0066U datasheet states. Does anybody have other measurements?
Thanks for any comments, Jürgen
Link to comment
Share on other sites
4 answers to this question
Recommended Posts
Archived
This topic is now archived and is closed to further replies.