National Instruments AT-MIO-16D, User Manual

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Chapter 4 Programming
© National Instruments Corporation 4-75 AT-MIO-16D User Manual
Programming the RTSI Switch
The RTSI switch can be programmed to connect any of the signals on the A side to any of the
signals on the B side and vice versa. To do this, a 56-bit pattern is shifted into the RTSI switch
by writing one bit at a time to the RTSI Switch Shift Register and then writing to the RTSI
Switch Strobe Register to load the pattern into the RTSI switch.
The 56-bit pattern is made up of two 28-bit patterns, one for side A and one for side B of the
RTSI switch. The low-order 28 bits select the signal sources for the B-side pins. The high-order
28 bits select the signal sources for the A-side pins. Each of the 28-bit patterns are made up of
seven 4-bit fields, one for each pin. The 4-bit field selects the signal source and the output
enable for the pin. Figure 4-1 shows the bit map of the RTSI switch 56-bit pattern.
A6 A5 A4 A3 A2 A1 A0 B6 B5 B4 B3 B2 B1 B0
A0 Control
Bit Number
Bit Number
55 51 47 43 39 35 31 27 23 19 15 11 7 3 0
MSB LSB
S2 S1 S0
31 30 29 28
OUTEN
Figure 4-1. RTSI Switch Control Pattern
In Figure 4-1, the fields labeled A6 through A0 and B6 through B0 are the 4-bit control fields for
each RTSI switch pin of the same name. The 4-bit control field for pin A0 is shown in Figure
4—1.
The bits labeled S2 through S0 are the signal source selection bits for the pin. One of seven
source signals can be selected. Pins A6 through A0 can select any of the pins B6 through B0 as
signal sources. Pins B6 through B0 select any of the pins A6 through A0 as signal sources. For
example, the pattern 011 for S2 through S0 in the A0 control field selects the signal connected to
pin B3 as the signal source for pin A0.
The bit labeled OUTEN is the output enable bit for that pin. If the OUTEN bit is set, the pin is
driven by the selected source signal (the pin acts as an output pin). If the OUTEN bit is cleared,
the pin is not driven regardless of the source signal selected; instead, the pin can be used as an
input pin.
If the A0 control field above contains the pattern 0111, the signal connected to pin B3 (Trigger
Line 3) appears at pin A0. On the AT-MIO-16D board, this arrangement allows the
EXTCONV* signal to be driven by Trigger Line 3. Conversely, if the B4 control field contains
the pattern 1011, the signal connected to pin A5 appears at pin B4. This arrangement allows
Trigger Line 4 to be driven by the AT-MIO-16D OUT1 signal. In this way, boards connected
via the RTSI bus can send signals to each other over the RTSI bus trigger lines.