Data Sheet

UM10204 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
User manual Rev. 6 — 4 April 2014 30 of 64
NXP Semiconductors
UM10204
I
2
C-bus specification and user manual
3.2.10 General call address
The general call address is for addressing every device connected to the I
2
C-bus at the
same time. However, if a device does not need any of the data supplied within the general
call structure, it can ignore this address. If a device does require data from a general call
address, it behaves as a slave-receiver. The master does not actually know how many
devices are responsive to the general call. The second and following bytes are received
by every slave-receiver capable of handling this data. A slave that cannot process one of
these bytes must ignore it. The meaning of the general call address is always specified in
the second byte (see Figure 30
).
There are two cases to consider:
• When the least significant bit B is a ‘zero’
• When the least significant bit B is a ‘one’
When bit B is a ‘zero’, the second byte has the following definition:
0000 0110 (06h) — Reset and write programmable part of slave address by hardware.
On receiving this 2-byte sequence, all devices designed to respond to the general call
address reset and take in the programmable part of their address.
0000 0100 (04h) — Write programmable part of slave address by hardware. Behaves as
above, but the device does not reset.
0000 0000 (00h) — This code is not allowed to be used as the second byte.
Sequences of programming procedure are published in the appropriate device data
sheets. The remaining codes have not been fixed and devices must ignore them.
When bit B is a ‘one’, the 2-byte sequence is ignored.
3.2.11 Software reset
Following a General Call, (0000 0000), sending 0000 0110 (06h) as the second byte
causes a software reset. This feature is optional and not all devices respond to this
command. On receiving this 2-byte sequence, all devices designed to respond to the
general call address reset and take in the programmable part of their address.
3.2.12 START byte
Microcontrollers can be connected to the I
2
C-bus in two ways. A microcontroller with an
on-chip hardware I
2
C-bus interface can be programmed to be only interrupted by requests
from the bus. When the device does not have such an interface, it must constantly monitor
the bus via software. Obviously, the more times the microcontroller monitors, or polls the
bus, the less time it can spend carrying out its intended function.
There is therefore a speed difference between fast hardware devices and a relatively slow
microcontroller which relies on software polling.
Fig 30. General call address format
002aag662
LSB
second byte
0 0 0 0 0 0 0 0 A X X X X X X X BA
first byte
(general call address)