BASIC stamp manual v2.2

5: BASIC Stamp Command Reference – OWIN
BASIC Stamp Syntax and Reference Manual 2.2 • www.parallax.com • Page 299
The 1-Wire protocol has a well-defined standard for transaction sequences.
Every transaction sequence consists of four parts: 1) Initialization, 2) ROM
Function Command, 3) Memory Function Command, and 4)
Transaction/Data. Additionally, the ROM Function Command and
Memory Function Command are always 8 bits wide (1 byte in size) and is
sent least-significant-bit (LSB) first.
The Initialization part consists of a reset pulse (generated by the master)
and will be followed by a presence pulse (generated by all slave devices).
Figure 5.20 details the reset pulse generated by the BASIC Stamp and a
typical presence pulse generated by a 1-wire slave, in response.
Figure 5.20: OWIN Reset and
Presence Pulse.
BASIC Stamp’s
Reset Pulse
Apx. 564 s
µ
Device’s
Presence
Pulse
60 - 240 s
µ
Resting State
15 - 60 s
µ
driven by BASIC Stamp
driven by 1-wire device
+5 (vdd)
0 (vss)
This reset pulse is controlled by the lowest two bits of the Mode argument
in the OWIN command. It can be made to appear before the ROM
Function Command (ex: Mode = 1), after the Transaction/Data portion (ex:
Mode = 2), before and after the entire transaction (ex: Mode = 3) or not at all
(ex: Mode = 0). See the section on Mode, above, for more information.
Following the Initialization part is the ROM Function Command. The
ROM Function Command is used to address the desired 1-Wire device.
Table 5.67 shows common ROM Function Commands. If only a single
1-Wire device is connected, the Skip ROM command may be used to
address it. If more than one 1-Wire device is attached, the BASIC Stamp
will ultimately have to address them individually using the Match ROM
command.
THE 1-WIRE PROTOCOL FORMAT.