BBC MICROCOMPUTER MODEL B
1770 DISC INTERFACE
UPGRADE KIT

Change from 1770 to 1772 disc controller chip

This upgrade kit now contains a 1772 Disc Controller chip,
which has suprseded the 1770 version.

The fitting and use of the module are identical to those for the
1770 version, with the exception that the setting of the
keyboard links (see Chapter 12 of the Disc Filing System
User Guide and Page 7 of Addendum 1 to the Guide) will
produce step times different from those defined in the
Addendum. The full table is now as follows:

	Link 3	Link 4	Step Time	Step Time
					   1772	   1770

	  0		  0		    6ms	   6ms
	  1		  0		   12ms	  12ms
	  0		  1		    2ms	  20ms
	  1		  1		    3ms	  30ms

You should avoid setting the step time of a standard 5 1/4 inch
disc drive to 2 or 3ms with the 1772 chip, as most of these
drives will not work at these speeds.

(c) Copyright Acorn Computers Ltd
Published by Acorn Computers Ltd
March 1989
Part No.0433, 080 Issue 1