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ULTRA MUTE
CIRCUIT DESCRIPTION
ULTRA MUTE is a microprocessor based system that stores and recalls specific mute states
on the SR40•8 console. The system uses a 12MHz 80C51 processor. The 80C51 CPU
produces a 14 bit address. The lower 8 bits are latched by a 74HC573 from the
multiplexed address/data bus. User presets are stored in a 24C65 non-volatile RAM.
To communicate with the console, the 80C51 CPU uses serial data sent along chains of
shift registers. There are three chains of shift registers;
LED, FET,
and
SWITCH
.
The serial-in-
parallel-out
LED
chain controls all mute LEDs, the Ultra Mute control panel LEDs, and
numeric display. The
FET
chain is also SIPO and controls the DG213 analog switch ICs,
which perform the actual signal path muting. The
SWITCH
chain is parallel-in-serial-out. It
scans all mute switches and Ultramute control switches. All serial data is sent along the
MUTE BUS.
MUTE BUS PIN OUT AN D FUN C TION
Pin # N am e
Functio n
1
LED D ATA
Serial data fo r all m ute LED s, co ntro l LED s and num eric display
2
LOAD LED Updates LED data to shift reg ister parallel o utputs
3
SW D ATA
Serial data fro m all m ute and co ntro l sw itches
4
LOAD SW
Updates sw itch data fro m shift reg ister parallel inputs
5
FET D ATA
Serial data fo r all FET analo g sw itches
6
LOAD FET
Updates FET data to shift reg ister parallel o utputs
7
C LOC K
Serial clo ck fo r sw itch data
8
n/c
9
P-C LOC K
Serial clo ck fo r LED and FET data
10
n/c
Obviously, it is critical that the mute bus is chained through the PCBs in the proper
sequence. The mute bus originates at the
MUTE CONTROL BOARD
, which contains the
CPU, EPROM, SRAM, NVRAM, UART and supporting IC’s. It next goes to the
MUTE SWITCH
BOARD
(daughter board of the master section) which contains all the Ultramute system
controls and numeric display. It continues to the
OUTPUT DIGITAL BOARD which
contains
the shift registers for the master section and also generates the solo clock. Finally, the
mute bus chains through all
CHANNEL BOARDS
in descending order. Each PCB in the
mute bus chain has designated MUTE BUS IN and MUTE BUS OUT connectors, no address
jumpers are required.
MIDI communication is handled directly by the 80C51 CPU. RS-232 communication is
processed by a 6850 UART. The UART clock comes from the factory set to 19.2K BAUD. It
can be modified to 9600 or 32.4K via JP1. For RS-232 communication, the SR40•8’s data
port uses a DB9 connector. Pin 3 is RDX (receiving line), pin 2 is TDX (transmitting line),
and pin 5 is ground (shield).
For complete MIDI implementation information, refer to the owner’s manual.
