Tektronix 2440, User Manual

Page: 64 / 531

Theory of O p e ra tio n - 2 4 4 0 Service
Table 3-3
Processor M iscellaneous R egister
(PM REG) O utput Functions
Bit Output Name O utput Function
0
MWPDN Masks off (disables) Waveform
Processor Done interrupt.
1
MSYNTRIG Masks off Synchronous Trigger
interrupt.
2
MFPINT Masks off Front-Panel interrupt.
3 STEP COMP
Indicates the AutoStep
Sequencer has com pleted a
sequence step.
4 SEQOUT Indicates the AutoStep
Sequencer has com pleted a
sequence.
6
BELL
Indicates an event occurred
which normally rings
instrument’s internal warning
bell.
WAVEFORM PROCESSOR SYSTEM
The Waveform Processor System (diagram 2) performs the
high-speed data-handling operations needed to produce
and update displays of acquired data points on the CRT
including averaging, enveloping, adding, m ultiplying, and
interpolation of the waveform data. It accepts task informa­
tion from the System
jjl
P and then carries out the assigned
tasks without further need of the System pR When that task
list has been completed, it sends an interrupt to the System
pP to inform it that another list of tasks can be accepted.
The Waveform pP memory space is accessible by the
System pR allowing the System pP to send commands to
the Waveform jxP and to read any desired result or data
location especially for the GPIB I/O functions.
W aveform
pP
Waveform pP U470 is a specially designed, high-speed
microprocessor with a 16-bit multiplexed data and address
bus and separate
12
-bit instruction-address and 16-bit
instruction-data busses. The Waveform pP is clocked at
2.5 MHz and executes one instruction each clock cycle.
Internally the Waveform pP uses a 32-bit wide instruction
word. Therefore, to enable it to obtain a complete instruction
for execution with each pP cycle, instructions are
“double-prefetched.” Two 16-bit halves of the instruction are
fetched from the instruction bus with each cycle at a 5 MHz
rate, so that the instruction words are 32 bits wide.
Initially, with power-on, WPRESET (Waveform pP reset) from
Processor Controlled Register U860 (diagram 1) will be LO,
holding the processor reset via U270C. This reset remains in
effect until the System pP writes a HI bit to the W PRESET
output of U860 to remove the reset and enable the Waveform
pR The System pP also holds the Waveform pP reset while
it is updating the command list in RAM of the next task that
the Waveform pP is to perform. This reset occurs at the
completion of each set of tasks given to the Waveform pP
and is released when the new task list is in place in the
Waveform pP Command RAM, U440.
Upon release of WPRESET, the Waveform pP fetches the
first two 16-bit words from its instruction ROMs, U480 and
U490, at a 5 MHz rate and forms them into a 32-bit instruc­
tion word. Waveform pP U470 then executes the first instruc­
tion and at the same tim e it “prefetches” the next 32-bit word
from the instruction ROM (the next instruction). The
Waveform pP continues fetching instructions to carry out its
internal initialization routine until that is com pleted, and it
then looks in Command RAM at a vectored location to find
the first task in the task list.
The first instruction in the task list tells the Waveform pP
what is to be done. The pP then switches to the routine in
ROM to get the instructions that do that job. Part of that
routine might be to get the arguments for the task. When the
arguments are in place, the Waveform pP then finishes the
task routine. When done with the first task, the Waveform pP
looks at the task list for the next task. It keeps doing the
commands and arguments for each task until the entire task
list is done. The last task of every task list is the W PDN task
(Waveform Processor Done). Upon receiving that task, the
Waveform pP sets the WPDN bit to the System pP Interrupt
circuit HI, informing the System pP that it is finished. It then
enters a ‘ loop forever” state to wait for its next set of instruc­
tions. When the System pP checks the interrupt register and
finds WPDN H i, it resets the Waveform pP and writes a new
list of tasks to the Waveform pP Command RAM.
3-22
R EV JU N 1991