GT-96100A Advanced Communication Controller
354
Revision 1.0
Unless otherwise specified:
‘1’ means set
‘0’ means unset.
‘0’ is the default value after reset.
14.6.5.1 CHR1 - SYNC/DLE Register (SDR)
CHR1[7:0] holds the SYNC character and CHR1[23:16] holds the DLE character for the channel. After reset it
holds the value of 7E in the SYNC field and FE in the DLE field. The user must write the appropriate values
before enabling the Rx/Tx machines.
If bit 15 is set, the BISYNC receive machine discards the SYNC patterns received in a middle of a message.
NOTE: This usually happens when the transmitter experiences underrun.
If bit [15] is ‘0’ the SYNC characters is transferred to the receive buffer.
If bit 31 is ‘1’, the first DLE received in transparent mode is discarded. If bit 31 is ‘0’, the BISYNC receiver is
not discard DLE in transparent mode.
A BISYNC transmitter always stuffs the leading DLE before transmitting the DLE that is part of a transparent
buffer (transmit descriptor with TR bit set). In order to send DLE ETX, for example, the CPU must either prepare
a buffer that contains DLE ETX and set TR=’0’, or prepare a buffer with ETX and program the transmitter to
send a leading DLE by setting the TD bit in the descriptor.
A BISYNC transmitter always transmits SYNC-SYNC at the beginning of a frame. This is true in MonoSYNC
and NibbleSYNC modes.
When a BISYNC transmitter experiences underrun it transmits continuous SYNC patterns in text mode or DLE-
SYNC in transparent mode. The BISYNC transmitter exits this state upon receiving new data or when the CPU
issues a Stop or Abort command.
The receiver SYNC length is programmable. The actual length is determined according to the value of the RSYL
bits in the MMCRx. If the RSYL bits equal #00b, the synchronization is done externally and the receiver will
start receiving when CD* is asserted.
In NibbleSync mode, bits [7:4] are used by the receiver for sync recognition. Bits [3:0] should return the SYNC
pattern in order to assure proper SYNC transmission.