SAB82538 Datasheet, PDF (81/253 Pages) Infineon Technologies AG – ICs for Communications

SAB 82538
SAF 82538
2.5.4 Special Functions
2.5.4.1 Preamble Transmission
If enabled via register CCR3, a programmable 8-bit pattern (register PRE) is transmitted
with a selectable number of repetitions after Interframe Timefill transmission is stopped
and a new frame is ready to be sent out.
Note: If the preamble pattern equals the SYN pattern, reception is triggered by the
preamble.
2.5.4.2 Continuous Transmission (DMA Mode only)
If data transfer from system memory to the ESCC8 is done by DMA (DMA bit in XBCH
set), the number of characters to be transmitted is usually defined via the Transmit Byte
Count registers (XBCH, XBCL: bits XBC11…XBC0).
Setting the “Transmit Continuously” (XC) bit in XBCH, however, the byte count value is
ignored and the DMA interface of ESCC8 will continuously request for transmit data any
time 32 new characters can be entered in XFIFO.
This feature can be used to transmit frames of length higher than the byte count specified
by XBCH, XBCL (frames with more than 4095 bytes).
Note: If the XC bit is reset during continuous transmission, the transmit byte count
becomes valid again, and the ESCC8 will request the amount of DMA transfers
programmed via XBC11…XBC0. Otherwise, the continuous transmission and the
generation of DMA input requests is stopped when a data underrun condition
occurs in XFIFO. Instead of CRC, continuous “1”-s (IDLE) are transmitted
thereafter.
2.5.4.3 CRC Parity Inhibit
If the internal CRC generator is not used for calculation of Frame Check Sequence, an
externally calculated checksum (16 bits) can be appended to the message frame without
internally generated parity information, although parity is enabled for data characters.
Prerequisites are:
q CRC generator disabled (CAPP = 0),
q CON = 0 for all data characters which are to be included into parity generation (normal
operation),
q CON = 1 for both bytes defining the CRC checksum,
q Message End indication has to be issued after the checksum is written to XFIFO.
The programmed character length has no influence on this function.
Semiconductor Group
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