Lexicon
7-45
3231
00
01
02
03
04
05
06
07
10 11 12 13 14
20 21
22
23 24
30 33 34
40
41
42
43
44
16
25
27
36
45 46
17
37
47
Lighted
Notes:
Num = ROW-COL
Figure 4-1 Keypad Rows and Columns
Keypad Leds (sheet 8)
There are 12 keys on the keypads that are lighted. The array of LEDs that illuminate the keypad is
organized for scanning as 4 rows by 4 columns. Under software control, the array is driven by sequentially
saturating one of the four column-driver transistors Q4-Q6. One output of U6 (74AC273) gets set to a logic
low to sink base current for one transistor through the associated base resistor R26-R29, while the other
three transistor control lines remain high, keeping the other transistors off. The transistor collectors drive the
column lines LED_G[3:0], sourcing the anodes of the LEDs the from the 5VD power rail. The cathodes of
each column of LEDs connect through current-limiting resistors R22-R25 to the remaining four outputs of
U6, the row drivers. Within a driven column, an LED lights when a row driver sinks current from its cathode.
Software asserts WR_KPD to load U6 with the appropriate sequence of row and column scanning patterns.
In reset, all LEDs will be lit, because all outputs of U6 are set low, sourcing all anodes via the transistors
and sinking current from all cathodes.
A/D Converters
There are two 8-channel 10-bit Analog-To-Digital converters (TLV1548M) on the main board. One is used
to get the position of the wiper arm on the 8 faders. The second takes care of the joystick, Lexicon button,
and the 12-volt sense.
A single 8-bit command register is implemented to enable the scanning of both A/Ds and to have direct
access to the A/D converters. When the enable command is given, the FPGA will do a continuous scan of
the inputs storing the values in the FPGA. The addressing of the two converters is interleaved allowing
faster updates of the values.
If the scanner is not enabled the command register will allow the selection of a single input or one of the
other commands. When the command is given software must wait at least 60 secs before reading the
value. The value of the selected input is stored in the register locations based on bits [3:0] of the command.
This means that one converter will overwrite the locations of the other when in this mode.
4.5. Motorized Faders
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