BASIC stamp manual v2.2

5: BASIC Stamp Command Reference – SHIFTIN

BASIC Stamp Syntax and Reference Manual 2.2 • www.parallax.com • Page 433

Here is a simple example:

result VAR Byte

SHIFTIN 0, 1, MSBPRE, [result]

Here, the SHIFTIN command will read I/O pin 0 (Dpin) and will generate

a clock signal on I/O 1 (Cpin). The data that arrives on 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 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:

resultLo VAR Word

resultHi VAR Nib

SHIFTIN 0, 1, MSBPRE, [resultHi\4, resultLo\16]

The above code will first shift in four bits into resultHi and then 16 bits into

resultLo. The two variables together make up a 20 bit value.

A SIMPLE SHIFTIN EXAMPLE.

ONTROLLING THE NUMBER OF BITS

RECEIVED