Parallax BASIC Stamp 2e, Programming Manual

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5: BASIC Stamp Command Reference – SHIFTIN
BASIC Stamp Programming Manual 2.0c
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Here is a simple example:
Result VAR BYTE
SHIFTIN 0, 1, MSBPRE, [ Result ]
Here, the SHIFTIN command will read I/O pin 0 (the Dpin) and will
generate a clock signal on I/O 1 (the Cpin). The data that arrives on the
Dpin depends on the device connected to it. Let's say, for example, that a
shift register is connected and has a value of $AF (10101111) waiting to be
sent. Additionally, let's assume that the shift register sends out the most
significant bit first, and the first bit is on the Dpin before the first clock
pulse (MSBPRE). The SHIFTIN command above will generate eight clock
pulses and sample the data pin (Dpin) eight times. Afterward, the Result
variable will contain the value $AF.
By default, SHIFTIN acquires eight bits, but you can set it to shift any
number of bits from 1 to 16 with the Bits argument. For example:
Result VAR BYTE
SHIFTIN 0, 1, MSBPRE, [ Result \4 ]
Will only input the first 4 bits. In the example discussed above, the Result
variable will be left with %1010.
Some devices return more than 16 bits. For example, most 8-bit shift
registers can be daisy-chained together to form any multiple of 8 bits; 16,
24, 32, 40... To solve this, you can use a single SHIFTIN instruction with
multiple variables. Each variable can be assigned a particular number of
bits with the Bits argument. As in:
ResultLow VAR WORD
ResultHigh VAR NIB
SHIFTIN 0, 1, MSBPRE, [ ResultHigh\4 , ResultLow\16]
The above code will first shift in four bits into ResultHigh and then 16 bits
into ResultLow. The two variables together make up a 20 bit value.
A
SIMPLE
SHIFTIN
EXAMPLE
.
C
ONTROLLING THE NUMBER OF BITS
RECEIVED
.