Status Bytes - Sequential PROPHET-5 Operation Manual

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6-3
STATUS BYTES
The
Prophet-5 never volunteers
DATA
FROM,
it
only transmits
when
prompted
by the
sequencer.
Communication
is
initiated
by
the
sequencer
transmitting
"status" bytes
which
may
or
may
not signify
that
data follows.
For example,
to
change programs
the
sequencer
first
sends a
byte
to the
Prophet
saying that the next byte
is
the
new
program number. The Prophet
will
then wait
for the
new
program
byte,
and change
its
program when
the
second byte
is
received.
There are 13 unique status bytes.
A
status byte
is
simply a unique hexadecimal
(H)
number.
It is
distinguished
from
other bytes
merely by
being the
first
which
the
sequencer transmits to the
Prophet
as part of
any data
transfer.
The
Prophet
requires
-
1-1/2 milliseconds (worst case) to respond
to
the status byte
interrupt.
It
will
then
be ready
to
receive
or
transmit data which
is
formatted and timed
as specified below.
Generally, while data can be transmitted with spaces of between
1
to
'f
ms
between
bytes without causing
errors,
you
will
probably
want
to
operate
faster
for
the
most
transparent operation.
Most
of the Prophet's receiving operations are accompanied
by
a "time-out"
which
declares an
error
if
data
is
not received within
*
ms.
When
any
error
is
detected, the
Prophet simply
ignores the received data and
resets to wait
for
another
status byte.
So
if
data arrives too
late,
or
you
accidentally send
more
data
than needed,
the
Prophet
may
interpret the data
as
a
status byte.
The
Prophet
will
not
accept
status bytes during
its
TUNE
routine.
During
TUNE,
DATA FROM
transmits a
BREAK
signal to
tell
the sequencer the Prophet
isn't
listening.
The
BREAK
is
simply a continuous low on
DATA
FROM.
In
other words, your
receiver
will
see a
start
bit
followed by no
stop
bit.
The
break can
therefore
be
detected by counting
at
least
two
framing
errors
with zero
as data
received.
(Provided that the receiver
is
being constantly clocked.) The
BREAK
can
therefore be
used
to inhibit
the sequencer.
6-4
STATUS
0:
SEND KEYBOARD
and
BANK/PROGRAM
BYTES
This status byte
is
used
for the
sequencer
to
record the Prophet's keyboard and
"sound"
program
status.
Code
01(H)
on
DATA TO
interrupts the
Prophet
to
read
its
keyboard.
After
a
-
2-ms
(worst-case) delay
to
respond
to
the
interrupt, the
Prophet
transmits
eight bytes of keyboard
information over
DATA
FROM.
As mapped
below, 61 of the
€>i^
bits
represent key
status (three aren't used).
means
the
key
is
off
("up"),
1
means
the
key
is
on
("down").
As
shown,
the least-significant bit (LSB) of the
first
byte
is
the
lowest
C
(CO).
LSB MSB
Byte CO
C#0
DO
D//0
EO FO F#0 GO
Byte
1
G#0 AO
A//0
BO CI C#l
Dl
D#l
Byte
2
El Fl
F#l Gl G#l Al A#l
Bl
Byte
3
C2
C#2 D2
D#2
E2 F2 F#2 G2
Byte
k
G//2
A2
A//2
B2 C3
C//3
D3 D#3
Byte
5
E3 F3
F#3 G3
G//3
A3
A//3
B3
Byte
6
CH C/M
m
mi*
E^
F^
F//*
G^
Byte
7
G#^
M
A//^
B4 C5
X
XX
CMIOOOD
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