Standard Software Supplied With Mpx-L; Basic Command Structure And Protocol; Opcode Byte - Lexicon MPX-1 Technical Manual

STANDARD SOFTWARE SUPPLIED WITH HPX-l
The HPX-l is supplied wi th an EPROM that contains some general purpose
utility routines. It contains code to initialize the interrupt controllers (to
a benign state). several useful subroutines and a general purpose command
interpreter that implements a "channel protocol". Included are several built-in
commands to perform useful tasks such as loading and executing programs from
system memory. changing the interrupt controller parameters and block memory
moves on system RAM. The command structure includes a sophisticated "link"
protocol that allows chaining of command sequences and recursion.
Note that no representation is made that this is the most efficient way to
program or use an MPX board. Rather. it is intended as partly tutorial and
partly a useful way to get "up and running" with the MPX in a minimum amount of
time.
What follows is a discussion of the basic command structure and then
descriptions of the actual commands. Following that is a discussion of the code
itself that explains how to add custom commands and describes several useful
subroutines.
BASIC COMMAND STRUCTURE AND PROTOCOL
When the MPX-1 powers up. it masks all its interrupt inputs, does some
internal initialization and waits quietly for an ATTN on its ATTN port. When it
receives an ATTN it will read in 16 bytes from the system memory starting at
address 50 hex. The meaning of the bytes follows:
Byte 0:
Byte 1:
Byte 2:
Byte 10:
Byte 11:
Byte 12:
Byte 13:
Byte 14:
Byte 15:
Opcode Byte
Status Indication Byte
General Purpos~,Parameter Byte 0
General Purpose Parameter Byte 8
Link Address (least significant byte)
Link Address
Link Address (most significant byte)
Result 1 byte
Result 2 byte
The following is a more detailed description of the bytes shown above:
OPCODE BYTE
The opcode byte contains the information that tells the MPX what command to
execute. and also contains two bits that control the completion interrupt and
link structures.
T~e
actual bit coding of the ope ode byte is shown below:
Bit 7
Bit 0
---------------------------------------------------------------
CONT
I
INT
I
o
I
BIT 4
I
BIT 3
I
BIT 2
I
BIT 1
I
BIT 0
I
---------------------------------------------------------------
12