Bisync Event Register - Motorola MC68302 User Manual

TD—Transmit DLE
0 = No automatic DLE transmission before the data buffer.
1 = The transmitter will transmit a DLE character before sending the data buffer, which
saves writing the first DLE to a separate data buffer when working in transparent
mode. The transmitter also checks for a DLE character in the middle of a buffer. If
found, it will insert an extra DLE (if the V-bit is set in the BISYNC SYNC register).
TR—Transparent Mode
0 = The transmitter will enter (remain in) the normal mode after sending the data buffer.
In this mode, the transmitter will automatically insert SYNCs in an underrun condi-
tion.
1 = The transmitter enters or remains in transparent mode after sending the data buff-
er. In this mode, the transmitter automatically inserts DLE-SYNC pairs in the un-
derrun condition. Underrun occurs when the BISYNC controller finishes a buffer
with L set to zero and the next BD is not available. The transmitter also checks all
characters before sending them; if a DLE is detected, another DLE is automatically
sent. The user must insert a DLE or program the BISYNC controller to insert it (us-
ing TD) before each control character required. The transmitter will calculate the
CRC16 BCS even if the BCS bit in the BISYNC mode register is programmed to
LRC. The PTCRC should be initialized to the CRC16 preset before setting this bit.
The following status bits are written by the CP after it has finished transmitting the associat-
ed data buffer.
UN—Underrun
The BISYNC controller encountered a transmitter underrun condition while transmitting
the associated data buffer.
CT—CTS Lost
CTS in NMSI mode or L1GR in IDL/GCI mode was lost during message transmission.
Data Length
The data length is the number of octets that the CP should transmit from this BD's data
buffer. It is never modified by the CP. The data length should be greater than zero.
Tx Buffer Pointer
The transmit buffer pointer, which always points to the first byte of the associated data
buffer, may be even or odd. The buffer may reside in either internal or external memory.
For correct operation of the function codes, the upper 8 bits of
the pointer must be initialized to zero.

4.5.13.12 BISYNC Event Register

The SCC event register (SCCE) is referred to as the BISYNC event register when the SCC
is programmed as a BISYNC controller. It is an 8-bit register used to report events recog-
MOTOROLA
NOTE
MC68302 USER'S MANUAL
Communications Processor (CP)
4-97