Parallax BASIC Stamp 2e Programming Manual page 305

2
2
e
Table 5.87: BS2, BS2e, BS2sx and
BS2p flow control pin states in
relation to polarity (inverted or non-
inverted).
U -
SING THE SERIAL TIME OUT
.
FEATURE
2
2
e
5: BASIC Stamp Command Reference – SEROUT
2 2
SerData VAR
sx p
SEROUT 1\0, 84, [SerData]
When SEROUT executes, I/O pin 1 (Tpin) is made an output, and I/O pin
0 (Fpin) is made an input, to wait for the "go" signal from the receiver.
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 5.35, 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.
In the flow control examples above, the only way the SEROUT instruction
will end (other than RESET or power-off) is if the receiver allows it to send
the entire OutputData list. If Fpin permission never occurs, the program is
stuck. However, you can tell the BASIC Stamp to abort SEROUT if it
doesn't receive Fpin permission within a specified time period. For
instance, to transmit a decimal number through pin 1 at 9600 baud, 8N,
inverted and abort SEROUT after 2 seconds (2000 ms) if no Fpin
permission arrives on I/O pin 0:
2 2
SEROUT 1\0, 16468, 2000, NoPermission, [DEC 150]
p
sx
STOP
NoPermission:
DEBUG CLS, "timed out"
If no Fpin permission arrives within 2 seconds, the program aborts
SEROUT and continues at the label NoPermission.
BYTE
Ready to Receive
("Go")
Inverted Fpin is High (1)
Fpin is Low (0)
BASIC Stamp Programming Manual 2.0c • www.parallaxinc.com • Page 303
Not Ready to Receive
("Stop")
Fpin is Low (0)
Fpin is High (1)