Roland MSQ-700 Service Notes page 7

SEP., 1984
MSQ-700
NOTE: MIDI clocks are not fed through IC29,
but contained in the MIDI data and are
selected by the program. Once selected, MIDI
clocks are processed by the CPU the same way
as clocks from the other sources.
CLOCK MULTIPLICATION
IC3 develops INT on every edge of CLK24
applied to DCDA terminal.The CPU ignores INT
occuring on the falling edge of CLK24. Upon
recognizing INT corresponding to the rising
edge of CLK24, the CPU reads and resets the
counter 2 in IC4 which in turn restarts
counting. The CPU sets the counter 2 counts
into counter 1 which generates rectangular
whose frequency 2.5 times that of CLK24 in
proportion to the ratio of the clocks coming
to both counters respectively:800kHz to 2MHz
— CLK24 x 2.5 = 60. Hereafter, call this
CLK60. When this CLK60 is applied to CTSA,
IC3 generates INT on every edge; this time
the CPU appreciates all the INTs and recog¬
nizes a chain of INTs as CLK120.
By observing some terminals, conversation
between IC1 and IC3 via INT line is examined
as exampled below.
This illustration has channel A representa¬
tive with Internal Clock OSC selected as an
interrupt source. For clarification on the
scope,no signal should be connected to chan¬
nel B (MIDI and DCB busses).
When IC3 receives a square wave at DCDA or
CTSA, it turns INT terminal low on every
edge.
Upon receiving INT, IC1 acknowledges it by
pulling MI and IORQ to low, causing IC3 to
turn INT back to high. While the CPU is per¬
forming a set of specified operations pre¬
programmed to handle each interrupt, IC3
keeps IEO (Interrupt Enable Out pin 7) low.
If INT is continuously high, IC3 is susp-
ective, it may not recognize the Internal
Clock.
If INT is continuously low, this time IC1
is suspectable; failing to recognize the
interrupt from IC3.
If IEO remains low, it is signaling that the
CPU cannot exit the routine involved with
interrupt. CPU, ROM, RAMs should be checked.
18 CTSA
j
III
j | 5 INT
1 - 15ys
u i i i i i y 7 ieo
-H I-*- -HM-
. 250ys 70ys
-10ms ( J = 250)-H
SYNC
Tempo clocks have been discussed in the pre¬
vious paragraphs. But with the MSQ-700
linked to external unit(s), synchronization
of start/stop and tempo is another important
consideration.
With Roland SYNC system ( especially SYNC
using DIN socket-- referred to as DIN SYNC),
the first tempo clock must be generated ( or
fed to slave ) after 5-10ms of a START
signal. INT CLOCK OSC on the Panel board
works to meet this specification. When the
MSQ-700 is ''started" with CLOCK set at INT,
IC2 PCI (Main board) goes low, which is in¬
verted at pin 6 of IC26 and resets INT CLOCK
OSC. After approxmately 5ms the OSC restarts
oscillation. The low from PCI is also in¬
verted at TR7 collector and applied to DIN
SYNC socket as a START signal. After approx¬
imately 5ms the first clock is output from
IC2 PC0 and routed to the DIN SYNC socket.
SYNC (DIN SYNC)
When SYNC is selected from the front panel,
START signal will be applied to PA0 of IC2
while clocks are to be fed to DCDA of IC3
after 5-10ms.
MIDI
The master CPU recognizes start when it re¬
ceives start message(llll 1010) through MIDI
bus and puts it into effect if CLOCK on the
panel is set at MIDI. The CPU recognizes
tempo clock via MIDI timing clock message.
However, if clock message comes too short
after a start signal, the CPU will fail to
read the first clocks.
The CPU processes timing clocks just the
same as it does for clocks from INT pins;the
CPU converts timing clocks into CLK120 via
counter 2, counter 1 and channel A loop.
TAPE
With TAPE selected by the CLOCK on the front
panel, the CPU recognizes start signal when¬
ever generated internally or externally and
will recognize the pulse from the FSK DEMO
as a tempo clock. This implies that some
mis interpretaion might be made at the CPU if
"START" is made before the leader tone comes
from the tape. The FSK DEMO is liable to
generate a pulse upon receiving a noise or
leader tone; this pulse is then might be re¬
cognized as the first tempo clock by the CPU.
To avoid this from happining, the CPU must
be fed with "START" while the leader tones
are being applied.
SYNC OUT
In PLAY or LOAD mode, the MSQ-700 provides
tempo clock for MIDI, TAPE SYNC and DIN SYNC
outputs. These outputs are, of course, the
duplication of clock source that is selected
from the front panel. With external clock
source selected, output on these sockets
delay behind the input 200us which is re¬
quired for the software to complete the
necessary job.
TAPE SYNC (FSK)
Clocks for TAPE OUT are routed from IC2 PC3
though TR4 to TR2 which, as it is turned ON
or OFF, shifts the frequency of TAPE SYNC
SIGNAL GENERATOR between 1.3kHz and 2.1kHz.
7