IBM AT 5170 Technical Reference page 183

Move Block BIOS
The Move Block BIOS was designed to make use of the memory
above the 1M address boundary while operating with IBM DOS.
The Block Move is done with the Intel 80286 Microprocessor
~
operating in the protected mode.
Because the interrupts are disabled in the protected mode, Move
Block BIOS may demonstrate a data overrun or lost interrupt
situation in certain environments.
Communication devices, while receiving data, are sensitive to
these interrupt routines; therefore, the timing of communication
and the Block Move should be considered. The following table
shows the interrupt servicing requirements for communication
devices.
Baud Rate 11 Bit (ms) 9 bit (ms)
300
33.33
30.00
1200
8.33 7.50
2400 4.16
7.50
4800 2.08
1.
87
9600
1.
04
0.93
Times are approximate
Communication Interrupt Intervals
The following table shows the time required to complete a Block
Move.
Buffer
Block Size Addresses
Time in ms
Normal
512 Byte
Both
even
0.98
Even and odd
1.
04
Both odd
1.
13
Maximum
64K Both Even
37.0
Even and odd
55.0
Both odd
72.0
Time is approximate
Move Block BIOS Timing
System BIOS 5-11