Parallax BASIC Stamp 1, Programming Manual

Page: 142 / 353

I2CIN - BASIC Stamp Command Reference
Page 140
•
BASIC Stamp Programming Manual 2.0b
•
www.parallaxinc.com
Special Formatter Action
STR ByteArray \L {\E}
Input a character string of length L into an array. If specified, an
end character E causes the string input to end before reaching
length L. Remaining bytes are filled with 0s (zeros).
WAITSTR ByteArray {\L}
Wait for a sequence of bytes matching a string stored in an array
variable, optionally limited to L characters. If the optional L
argument is left off, the end of the array-string must be marked
by a byte containing a zero (0).
SKIP Length Ignore Length bytes of characters.
The I
2
C protocol has a well-defined standard for the information passed at
the start of each transmission. First of all, any information sent must be
transmitted in units of 1 byte (8-bits). The first byte, we call the SlaveID, is
an 8-bit pattern whose upper 7-bits contain the unique ID of the device
you wish to communicate with. The lowest bit indicates whether this is a
write operation (0) or a read operation (1). Figure 5.7 shows this format.
The second byte, immediately following the SlaveID, is the Address. It
indicates the 8-bit address (within the device) containing the data you
would like to receive.
Some devices require more than 8 bits of address. For this case, the
optional LowAddress argument can be used for the low-byte of the required
address. When using the LowAddress argument, the Address argument is
effectively the high-byte of the address value. For example, if the entire
address value is 2050, use 8 for the Address argument and 2 for the
LowAddress argument (8 * 256 + 2 = 2050).
Following the last address byte is the first byte of data. This data byte may
be transmitted or received by the BASIC Stamp. In the case of the I2CIN
command, this data byte is transmitted by the device and received by the
BASIC Stamp. Additionally, multiple data bytes can follow the address,
depending on the I
2
C device. Note that every device has different
limitations regarding how may contiguous bytes they can receive or
transmit in one session. Be aware of these device limitations and program
accordingly.
T
HE
I
2
C
PROTOCOL FORMAT
.
Table 5.18: I2CIN Special
Formatters.
Figure 5.7: SlaveID Format.
7
A
6
6
A
5
5
A
4
4
A
3
3
A
2
2
A
1
1
A
0
0
R/W
U
SING
L
ONG ADDRESSES
.