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Running the
Host Compatibility Test
M16
Allen-Bradley Parts
Allen-Bradley has taken several measures to facilitate proper data transfer
between an IBM PC and the KTx across the ISA bus. We implemented a
byte swapper on the application-specific integrated circuit (ASIC) that
drives both byte lanes of the ISA bus with odd-byte data during an
odd-byte read of the dual port, i.e., SBHE=0, A0=1. This would allow
M16 to be missed on odd-byte reads in 'current', i.e., circa 1993, systems
without problems. Conversely, current host systems drive both the high
and low data lanes on odd-byte writes where the host does not see M16.
This diagnostic lets you test the system in which the KTx is installed to see
if it operates as a current system. Current systems will drive both byte
lanes with odd-byte data during an odd-byte write where the system does
not see M16 asserted by the slave card.
Important: If you run your card in 8-bit mode only, you do not have to run
M16 diagnostics.
M16 Diagnostics
This diagnostic uses the extended M16 test mode of the KTx ASIC. This
test mode is operational only when the KTx is in extended M16 mode. The
test mode turns off operation of the M16 line while operating the KTx
ASIC in the same manner as if M16 were being properly asserted. This
lets us determine if the high byte lane of the PC is being driven on an odd
bye write when M16 is not seen by the system. If the high byte lane is not
being driven, then the PC cannot be used in extended M16 mode and the
user must select standard M16 mode or 8-bit mode.
Important: Standard M16 mode is not implemented by any current
application programming interfaces (APIs) for the KTx. That is, no current
host software changes the KTx from its default extended M16 mode to
standard M16 mode. This mode is basically a safety net in case a user is
encountered who has incompatible hardware and cannot or will not use
8-bit mode.
Chapter 2
Start up and Shutdown
2-7
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