Shiftin - Parallax BASIC Stamp 2e Programming Manual

2
2
e
Table 5.89: SHIFTIN Quick Facts.
5: BASIC Stamp Command Reference – SHIFTIN

SHIFTIN

2 2
SHIFTIN Dpin, Cpin, Mode, [ Variable {\Bits} {, Variable {\Bits}...} ]
sx p
Function
Shift data in from a synchronous serial device.
• Dpin is a variable/constant/expression (0 – 15) that specifies the I/O
pin that will be connected to the synchronous serial device's data
output. This pin will be set to input mode.
• Cpin is a variable/constant/expression (0 – 15) that specifies the I/O
pin that will be connected to the synchronous serial device's clock
input. This pin will be set to output mode.
• Mode is a variable/constant/expression (0 – 3), or one of four
predefined symbols, that tells SHIFTIN the order in which data bits
are to be arranged and the relationship of clock pulses to valid data.
See Table 5.90 for value and symbol definitions.
• Variable is a variable in which incoming data bits will be stored.
• Bits is an optional variable/constant/expression (1 – 16) specifying
how many bits are to be input by SHIFTIN. If no Bits entry is given,
SHIFTIN defaults to 8 bits.
Quick Facts
Timing of T and t
h
Transmission Rate
Explanation
SHIFTIN and SHIFTOUT provide an easy method of acquiring data from
synchronous serial devices. Synchronous serial differs from asynchronous
serial (like SERIN and SEROUT) in that the timing of data bits (on a data
line) is specified in relationship to clock pulses (on a clock line). Data bits
may be valid after the rising or falling edge of the clock line. This kind of
serial protocol is commonly used by controller peripherals like ADCs,
DACs, clocks, memory devices, etc.
At their heart, synchronous-serial devices are essentially shift-registers;
trains of flip-flops that pass data bits along in a bucket brigade fashion to a
BS1 BS2 BS2e BS2sx BS2p
BS2
14 µs / 46 µs 14 µs / 46 µs
l
~16 kbits/sec ~16 kbits/sec
BASIC Stamp Programming Manual 2.0c • www.parallaxinc.com • Page 309
BS2e BS2sx
5.6 µs / 18 µs
~42 kbits/sec
BS2p
5.6 µs / 18.8 µs
~42 kbits/sec