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AST RESEARCH, INC.         TECHNICAL BULLETIN # 1361                 11-9-95

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              Ascentia 900N Hangs Due to 16 bit Serial Port Reads


PROBLEM

When attempting to make a single 16-bit access from an odd-aligned I/O port 
address, using a programming language such as Borland's C++, the Ascentia 
900N system may hang.


CAUSE

Certain inherent properties of the VLSI chipset, when used in the Ascentia 
900N system, cause this type of access to fail.


SOLUTION

To avoid this problem, program code should not support non-aligned 16 bit 
I/O transactions.  Since contiguous I/O registers are not common,  non-
aligned 16 bit I/O transactions are not likely to happen.  
For programmers, this means making two 8-bit reads from sequential 
registers rather than a single 16-bit read.


SYSTEMS AFFECTED
AST PART NUMBER AND DESCRIPTION

501299-XXX      Ascentia 900N 4/75 STN
501300-XXX      Ascentia 900N 4/75 TFT
501302-XXX      Ascentia 900N 4/75 STN
501304-XXX      Ascentia 900N 4/75 TFT