Parallax BASIC Stamp 2e Programming Manual page 291

2
2
e
Table 5.78: BS2, BS2e, BS2sx and
BS2p flow control pin states in
relation to polarity (inverted or non-
inverted).
5: BASIC Stamp Command Reference – SERIN
the rules of other serial handshaking schemes, but most computers other
than the BASIC Stamp cannot start and stop serial transmission on a byte-
by-byte basis. That's why this discussion is limited to communication
between BASIC Stamps.)
Here's an example using flow control on the BS2 (data through I/O pin 1,
flow control through I/O pin 0, 9600 baud, N8, noninverted):
2 2
SerData VAR
sx p
SERIN 1\0, 84, [SerData]
When SERIN executes, I/O pin 1 (Rpin) is made an input in preparation
for incoming data, and I/O pin 0 (Fpin) is made output low, to signal "go"
to the sender. After SERIN finishes receiving, I/O pin 0 goes high to tell
the sender to stop. If an inverted BaudMode had been specified, the Fpin's
responses would have been reversed. Here's the relationship of serial
polarity to Fpin states.
Non-inverted
See the Demo Program, below, for a flow control example using two BS2s.
In the demo program example, without flow control, the sender would
transmit the whole word "HELLO!" in about 6 ms. The receiver would
catch the first byte at most; by the time it got back from the first 1-second
PAUSE, the rest of the data would be long gone. With flow control,
communication is flawless since the sender waits for the receiver to catch
up.
In Figure 5.33, I/O pin 0, Fpin, is pulled to ground through a 10k resistor.
This is to ensure that the sender sees a stop signal (0 for inverted
communications) when the receiver is being programmed.
BYTE
Ready to Receive
("Go")
Inverted Fpin is High (1)
Fpin is Low (0)
BASIC Stamp Programming Manual 2.0c • www.parallaxinc.com • Page 289
Not Ready to Receive
("Stop")
Fpin is Low (0)
Fpin is High (1)