peb20525 Infineon Technologies Corporation, peb20525 Datasheet - Page 72

• Manufacturer Part Number: peb20525
• Description: 2 Channel Serial Optimized Communication Controller For Hdlc/ppp
• Manufacturer: Infineon Technologies Corporation

3.2.7
Beside the point-to-point configuration, the SCC 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, data transmission can be initiated by
each station over a common transmit line (bus). In case more than one station attempts
to transmit data simultaneously (collision), the bus has to be assigned to only one
station. A collision-resolution procedure is implemented in the SCC. Bus assignment is
based on a priority mechanism with rotating priorities. This allows each station a bus
access within a predetermined maximum time delay (deterministic CSMA/CD), no
matter how many transmitters are connected to the serial bus.
Prerequisites for bus operation are:
• NRZ encoding
• ‘OR’ing of data from every transmitter on the bus (this can be realized as a wired-OR,
• Feedback of bus information (CxD input).
The bus configuration is selected via bitfield SC(2:0) in register CCR0H.
Note: Central clock supply for each station is not necessary if both the receive and
The bus configuration mode operates independently of the clock mode, e.g. also
together with clock mode 1 (receive and transmit strobe operation).
3.2.8
The idle state of the bus is identified by eight or more consecutive ‘1’s. When a device
starts transmission of a frame, the bus is recognized to be busy by the other devices at
the moment the first ‘zero’ is transmitted (e.g. first ‘zero’ of the opening flag in
HDLC mode).
After the frame has been transmitted, the bus becomes available again (idle).
Note: If the bus is occupied by other transmitters and/or there is no transmit request in
3.2.9
During the transmission, the data transmitted on TxD is compared with the data on CxD.
In case of a mismatch (‘1’ sent and ‘0’ detected, or vice versa) data transmission is
immediately aborted, and idle (logical ‘1’) is transmitted.
Data Sheet
using the TxD open drain capability)
transmit clock is recovered by the DPLL (clock modes 3a, 7a). This minimizes the
phase shift between the individual transmit clocks.
the SCC, logical ‘1’ will be continuously transmitted on TxD.
SCC Serial Bus Configuration Mode
Serial Bus Access Procedure
Serial Bus Collisions and Recovery
72
Functional Overview
PEB 20525
PEF 20525
2000-09-14