Lexicon MPX-1 User Manual

Bits 0 through 4 of the opcode contain the "command number" of which there
are a possible 31 (one command is reserved). The first 10 commands have already
been defined and the remaining 21 may be implemented by you.
Command "OF" is reserved, and if invoked will be translated internally to a
NOP command.
The INT
bit (bit 6) of the opcode byte is the INTERRUPT ENABLE bit. If
this bit is set to one in the opcode, the MPX will cause an interrupt (SOD
interrupt) when it has completed the command. If this bit zero, an interrupt
will not be generated when the command has completed execution. Note that in
order for the interrupt to make it to the bus, it must be jumpered to an inter-
rupt line (see the hardware configuration section of this document for further
details) •
The CONT bit (bit 7) of the opcode byte is the CONTINUE bit and is asso-
ciated with the link structure. If the CONT bit is set high, execution of the
next command (pointed to by the link address) will commence immediately after
execution of the current command is complete. If the CONT bit is zero, the MPX
will stop when execution of the current command is complete, and wait for
another ATTN before executing the next command.
There are two considerations when using the CONT bit.
the INT bit is ignored if the CONT bit is set. This means
will only occur if no command is to follow, which is the way
want things to happen when executing a sequence of commands.
The
firs!.. is that
that
an interrupt
one would normally
Secondly, if the link address points to the beginning of this same instruc-
tion (pointing to itself) and the CONT bit is set, endless execution of the
instruction will occur. This could be useful. The way to stop execution would
be to change the opcode so that the CONT bit is zero. The opcode could be
changed to a NOP, or merely the same opcode wi th the CONT bi t zeroed. Ei ther
the system CPU or the MPX could change the opcode. DO NOT try to change the
link address on the fly! .,
Bit 5 is unused and is really a "don't care" bit, but a good practice would
be to always set this bit to zero.
STATUS INDICATION BYTE
This byte is used to "handshake" with the MPX when the use of a completion
interrupt is not desired, or they may be used in conjunction. This byte should
be set to zero before an ATTN is sent to the MPX. When the MPX is done
executing the command, it will set this byte to FF hex. In a non-interrupt
environment, this byte should be checked before another command is sent to the
MPX.
If the CONT bit is set in the command opcode, the status byte for that
particular command will NOT be set to FF hex. This means that in a sequence of
commands, only the status byte in the last command (the one with CONT = 0) will
be set to FF hex •
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Lexicon MPX-1 Specifications

General

Brand	Lexicon
Model	MPX-1
Category	Recording Equipment
Language	English