11/05     11/10       DATA PATHS M7260

M7260 KD11-B Data Path Module

The M7260 contains the clock circuit for the Serial Communication Line (SCL).

SCL baudrate adjustment

On the M7260 module is at the upper left corner (see the picture) a rotary switch to set the desired baudrate of the terminal connected on the SCL. See the table below for the available baudrates with the corresponding switch settings.
You can connect an oscilloscope or a frequency counter to the E02 D2 pin on the backplane to measure the clock. The table lists the period time that you can count on the grid of the oscilloscope. The frequency read-out on the frequency counter should be 16 times the desired baudrate.

-- RANGE 1 ---- RANGE 2 --

If the measured value is too far off from the correct value, or you see garbage characters on the terminal, you can adjust the clock rate with the potentiometer near the rotary switch at the edge of the board.
To adjust the SCL clock to the desired baud rate, do the following steps.

  1. Switch the computer off (...)!
  2. Disconnect the Berg header connector to the console.
  3. Remove the M7260 module from the backplane.
  4. Set the baud rate adjustment switch S1 to the position as indicated in the table.
  5. Install the M7260 module, connect the flatcable of the console and turn on the power.
  6. Connect an oscilloscope or frequency counter to the pin E02 D2 on the backplane.
  7. Adjust the potentiometer R29 to get the correct baud rate.
Since the screw of the potentiometer is at the edge of the M7260 board, you can also adjust the clock rate while the machine is running.
500    005000
502    105737
504    177564
506    100375
510    110037
512    177566
514    105200
516    000771
Just enter the small program from address 000500.
The start address is also 000500.
The little program will loop continuously until halted with the HALT switch. The program prints a continuous stream of characters.
Adjust R21 (the potentiometer) to the center of the range for which satisfactory characters are printed.

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