I2C-Interface Philips Semiconductors / NXP Semiconductors, I2C-Interface Datasheet - Page 8

• Manufacturer Part Number: I2C-Interface
• Description: Programming the 12C Interface
• Manufacturer: Philips Semiconductors / NXP Semiconductors

Philips Semiconductors
Expbriig
IC
ing as examples, the address is OlOOxxx.
The xxx indicates the address selected
by the state of the three address pins on
eight bits of data from the transmitter
followed by a ninth
ceiver. The first step in any PC data
slave on the SDA line. This act might
seem confusing, since we seem to be
01ooo0O1
the peripheral.
transfer is to send the address of the
mixing 7-bit addresses with g-bit data.
In practice, it’s quite easy to work with:
addresses are always seven bits long,
and the eighth bit is used to determine
whether the operation is a read or a
write. For example, upon transmitting
suming it exists on the bus and is
strapped to address
with a low on the SDA line after the
data bit. The master leaves the line
dress
is driven to the data level when the SCL
SCL is high. This protocol leads to a
master has finished with its last (eighth)
high. If it doesn’t find a slave with ad-
high and a failed communication at-
tempt can be detected.
ting data on the SDA line as soon as it
has detected that the eighth bit is set
(which is a read request). The SDA line
line is low. Data is read when SCL is
high, so SDA must not change when
2
l*C Specific information
PC serial transactions
If a slave is connected, it begins put-
10000,
to the
the
PCF8574, the slave, as-
data line ~111 remain
ACK
Ooo,
bit from the re-
will
are always
respond
EMBEDDED
0 I991 MILLER
simple definition of the start of an PC
transaction-SDA
simple to detect: SDA goes from low to
collector PC peripheral wants access to
low
high when SCL is high. This cycle
leaves SDA and SCL in the high state,
which is necessary if any other open-
the
and stop conditions of an FC bus
ADDITIDNAL
transaction.
even if you’re not using a processor that
directly implements it. If you’re not
planning to use Philips/Signetics
croprocessors with onboard PC support
of the 805 1 family), you can still use the
wide variety of available peripheral
chips.
using the PC serial bus is increasing all
A
(such as the 68070 or various members
the time. Application-oriented
grated circuits that support PC include
a voice sythesizer, a transc&er
remote control, several digital tuning
circuits for computer-controlled
sion, several audio processors, PLL fre-
quency synthesizers, tone generators,
and frequency synthesizers. General-
The
The number of integrated circuits
SYSTEMS
when the clock is high.
bus.
Reprinted
end of a transaction is equally
Figure 2 illustrates the start
s
is easy to work with and rela-
tively simple to implement,
you’ve seen, the PC protocol
DESIGN RDDTES
FREEMAN
with permission from
PROGRAMMING,
goes from high to
76
PUBLICATIONS
for IR
televi-
inte-
mi-
September
gineers. Sarns is also a founding mem-
purpose integrated circuits using PC in-
clude LCD drivers, digital-toanalog
converters, SRAMs, EEPROMs, and a
RAM clock/calender.
Philips has been aggressively marketing
this flexible method of extending pe-
ripheral support to control projects, and
it is currently catching fire on this side
of the Atlantic. It seems reasonable to
expect that, given the burden of printed-
wire requirements
tems based on increasingly wider chip
buses, more and more designers seeking
economy of means will be attracted to
the economy of PC.
Steven Sarns is the president of Vesta
is a member of Mensa, Intertel, and the
Michigan Society of Professional En-
ber of the Denver chapter of the Forth
Interest Group.
Jack Woehr is a senior project manager
at Vesta Technology Inc, in Wheat
Ridge, Colo. He is a Chapter Coordin-
atorfor the Forth Interest Group and is
currently a member of the X3Jl4 Tech-
nical committeefor
be reached by E-mail as [e-mail]
Technology in Wheat Ridge, Cola, He
.ca.us or as VESTA on GEnie.
PC is very popular in Europe, where
1991
ANS Forth. He can
for embedded sys-
Exploring l*C