STAMP 2 Communications And Control Projects.pdf

NETWORKING STAMP 2’S 29
I/O
VSS
(GND)
I/O
VSS
(GND)
I/O
VSS
(GND)
STAMP 2 STAMP 2 STAMP 2
1 2 3
Figure 2-13
STAMP 2 network open/noninverted baudmode.
+5V
1K
I/O VSS I/O VSS I/O VSS
STAMP 2 STAMP 2 STAMP 2
1 2 3
Figure 2-14
STAMP 2 network open/inverted baudmode.
party line network. Open baudmodes can actively drive the Serout pins only in one state; in
the other state they disconnect the I/O pin. Since the open baudmodes drive only in one state
and float in the other, there’s no chance of shorting the I/O pins. Note the polarity selected for
Serout determines which state is driven and which is open; see Table 2-2. Since the open baudmodes
drive to only one state, they need a resistor to pull the network into the other state, as
shown in Figs. 2-13 and 2-14.
Open baudmodes allow the STAMP 2 to share a party line, but it is up to the software to
resolve other network problems, such as who talks when and how to prevent data errors. In
the example in Fig. 2-15, and in the programs illustrated in BSNET1.BS2 and BSNET2.BS2
(Listings 2-1 and 2-2) the two STAMP 2’s share a party line. They monitor the serial line for
a specific word (“Yin” or “Yang”) and then transmit data. A personal computer can be used
to monitor the net activity via a line driver or CMOS inverter, as shown in Fig. 2-15. The
result of the two programs BSNET1.BS2 and BSNET2.BS2 is that a monitoring PC would