SAB
SAB
SAF
SAF
5.3 Bus Configuration
82525
82526
82525
82526
Beside the point-to-point configuration, the HSCX effectively supports point-to-multipoint (pt-
mpt, or bus) configurations by means of internal idle and collision detection/collision resolution
methods.
In a pt-mpt configuration, comprising a central station (master) and several peripheral stations
(slaves), or in a multimaster configuration (see
figure 6),
data transmission can be initiated by
each station over a common transmit line (bus). In case more than one station attempt to
transmit data simultaneously (collision), the bus is assigned to one station by a collision-
resolution procedure implemented by the HSCX. The bus assignment function is based on a
priority principle with both fixed and rotating priorities that enables each station to access the
bus in a predeterminable time. As a result, any number of transmitters can be connected to the
serial bus.
Prerequisites for bus operation are:
– NRZ encoding
– OR connection of data at the bus
– feedback of bus information (C
×
DA/C
×
DB input)
The bus configuration is selected via the CCR1 register.
Note:
Central clock supply for each station is not necessary if both the receive and transmit
clock is recovered by the DPLL (clock mode 7). In this case, the function of the DPLL
also minimizes the phase shift between the transmit clocks of the individual transmitters
so that an opening flag sequence will be sufficient to allow a correct collision detection.
The bus mode can be operated independently of the clock mode, e.g. also during clock
mode 1 (receive and transmission strobe) or clock mode 5 (programmable time-slots).
Semiconductor Group
60
SIEMENS [ Siemens Semiconductor Group ]
