610 Board's RX - CLK/Data circuit - Incorrect Resistor?
Posted: Fri Nov 10, 2023 8:14 pm
Hello All...
I have a 610 board which I am going through the calibration steps for the TX and RX (data/clk) timing adjustment via R9, R10, R18 and R19 pots.
This is for a 5 1/4" floppy drive.
The TX Data and TX Clock were fine. No issues.
The RX Clock calibration is good as well.
However, adjusting R19 to set the RX DATA negative pulse width to 6us, does nothing.
In fact, the pulse width doesn't change through the whole range of the pot R19. It sits around 8us whilst adjusting R19.
Just as a sanity check, I calculated the one-shot pulse width time based on the min/max Rext and Cext from the 610 schematic, and there is no way that these component values can reach 6us.
So, I did some research on other OSI floppy I/F boards and everything I could find had the same values for the Rext and Cext to achieve the 6us pulse width.
To achieve the 6us pulse width:
Rext should be 13K ohms (R19+R20)
If I set R20 = 8.2K and R19 = 10K, then I can dial in the 6us pulse width.
So, my questions are:
1) Does anyone have the 'actual' value for R20?
2) Is the RX DATA pulse width calibration suppose to be 6us? or something else.
Thanks
Andy
I have a 610 board which I am going through the calibration steps for the TX and RX (data/clk) timing adjustment via R9, R10, R18 and R19 pots.
This is for a 5 1/4" floppy drive.
The TX Data and TX Clock were fine. No issues.
The RX Clock calibration is good as well.
However, adjusting R19 to set the RX DATA negative pulse width to 6us, does nothing.
In fact, the pulse width doesn't change through the whole range of the pot R19. It sits around 8us whilst adjusting R19.
Just as a sanity check, I calculated the one-shot pulse width time based on the min/max Rext and Cext from the 610 schematic, and there is no way that these component values can reach 6us.
So, I did some research on other OSI floppy I/F boards and everything I could find had the same values for the Rext and Cext to achieve the 6us pulse width.
To achieve the 6us pulse width:
Rext should be 13K ohms (R19+R20)
If I set R20 = 8.2K and R19 = 10K, then I can dial in the 6us pulse width.
So, my questions are:
1) Does anyone have the 'actual' value for R20?
2) Is the RX DATA pulse width calibration suppose to be 6us? or something else.
Thanks
Andy