Actel Fusion Mixed-Signal FPGAs
ADC Input Multiplexer
At the input to the Fusion ADC is a 32:1 multiplexer. Of the 32 input channels, up to 30 are user
definable. Two of these channels are hardwired internally. Channel 31 connects to an internal
temperature diode so the temperature of the Fusion device itself can be monitored. Channel 0 is
wired to the FPGA’s 1.5 V VCC supply, enabling the Fusion device to monitor its own power supply.
Doing this internally makes it unnecessary to use an analog I/O to support these functions. The
balance of the MUX inputs are connected to Analog Quads (see the "Analog Quad" section on
page 2-84). Table 2-39 defines which Analog Quad inputs are associated with which specific analog
MUX channels. The number of Analog Quads present is device-dependent; refer to the family list in
the "Fusion Family" table on page I of this datasheet for the number of quads per device.
Regardless of the number of quads populated in a device, the internal connections to both VCC and
the internal temperature diode remain on Channels 0 and 31, respectively. To sample the internal
temperature monitor, it must be strobed (similar to the AT pads). The TMSTBINT pin on the Analog
Block macro is the control for strobing the internal temperature measurement diode.
To determine which channel is selected for conversion, there is a five-pin interface on the Analog
Block, CHNUMBER[4:0], defined in Table 2-40 on page 2-102. Table 2-39 shows the correlation
between the analog MUX input channels and the analog input pins.
Table 2-39 • Analog MUX Channels
Analog MUX Channel
Signal
Vcc_analog
AV0
AC0
Analog Quad Number
0
1
Analog Quad 0
2
3
AT0
4
AV1
AC1
Analog Quad 1
Analog Quad 2
Analog Quad 3
Analog Quad 4
Analog Quad 5
Analog Quad 6
5
6
AT1
7
AV2
AC2
8
9
AT2
10
11
12
13
14
15
16
17
18
19
20
21
AV3
AC3
AT3
AV4
AC4
AT4
AV5
AC5
AT5
AV6
AC6
AT6
Preliminary v1.7
2-101
ACTEL [ Actel Corporation ]
