A Reset - Alesis QS Series Service Manual

shows that knowing how the hardware is supposed to respond to software changes can greatly
simplify the task of hardware troubleshooting.
The most important pins are:
D0-D16
A0-A23
RES
RD
HWR
XTAL, EXTAL Input for system clock crystal.
PX.X
TXD1
TXD2
RXD1
RXD2
PITCH
DATA
MOD
RES
CD1
CD2
PC/MAC
KEYINT
SUS
SMUTE
EDIT PCB SWITCH MATRIX (See Section 2.31C).

2.31A RESET

Reset is one of the single most important circuits/signals in the entire unit. Without a
correct RST signal during power up and power down, any number of problems can occur.
These can range from an occasional failure such as an odd audio "blip", to complete, system
wide lock ups and data corruption. Therefore any time processor problems are suspected, RST
should be the first thing checked.
In order to ensure that data will not be corrupted, the reset circuit uses the raw power
supply signal to determine the correct time to assert the RST signal (i.e. not until the regulated
+5V supply rail contains no ripple). This is done by using a raw supply threshold of
approximately 7V. Since the power down sequence of events is generally the reverse of the
power up process, only the power up events are described here.
Alesis QS Series Keyboards Service Manual V1.00
16 Bit Data Buss (note that in the QS Series some of the other
devices only use 8 bits of the data buss. This may cause some
noise in the unused data lines during processor reads making
the appear "bad" due to a floating input. While ignored by the
software, it can make troubleshooting a real open in the data
buss more difficult.
23 Bit Address Buss (Note that only 20 bits are actually used).
System RESET line. Asserted only during power up/down. (See
Section 2.31A)
Read Enable
Write Enable
I/O Ports are configured by the software and allow the software
some direct hardware access. In particular are:
Transmit Serial Data line to MIDI output circuit (See Section 2.31D).
Transmit Serial Data line to PC/MAC output circuit (See Section 2.50).
Receive Serial Data line From MIDI In circuit (See Section 2.31D).
Receive Serial Data line From PC/MAC input circuit (See Section 2.50).
Pitch Wheel data input (See Section 2.31C).
Data Slider data input (See Section 2.31C).
Mod Wheel data input (See Section 2.31C).
PCMCIA Card #1 Present Switch input (See Section 2.32B).
PCMCIA Card #2 Present Switch input (See Section 2.32B).
PC/MAC Serial Port Switch input (See Section 2.50).
Keyscan ASIC interrupt .input (See Section 2.33).
Sustain Pedal Input.
DAC Output Mute
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11/19/06