MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 151

• Manufacturer Part Number: MC68000
• Manufacturer: MOTOROLA [Motorola, Inc]

ENR—Enable Receiver
ENT—Enable Transmitter
MODE1–MODE0—Channel Mode
4.5.4 SCC Data Synchronization Register (DSR)
Each DSR is a 16-bit, memory-mapped, read-write register. DSR specifies the pattern used
in the frame synchronization procedure of the SCC in the synchronous protocols. In the
UART protocol it is used to configure fractional stop bit transmission. After reset, the DSR
defaults to $7E7E (two FLAGs); thus, no additional programming is necessary for the HDLC
protocol. For BISYNC, DDCMP, and V.110, the contents of the DSR should be written be-
fore the channel is enabled. Note that for the DDCMP, SYN1 must equal SYN2 must equal
DSYN1 for proper operation.
MOTOROLA
When ENR is set, the receiver is enabled. When it is cleared, the receiver is disabled, and
any data in the receive FIFO is lost. If ENR is cleared during data reception, the receiver
aborts the current character. ENR may be set or cleared regardless of whether serial
clocks are present. To restart reception, the ENTER HUNT MODE command should be
issued before ENR is set again.
When ENT is set, the transmitter is enabled; when ENT is cleared, the transmitter is dis-
abled. If ENT is cleared, the transmitter will abort any data transmission, clear the transmit
data FIFO and shift register, and force the TXD line high (idle). Data already in the trans-
mit shift register will not be transmitted. ENT may be set or cleared regardless of whether
serial clocks are present.
The STOP TRANSMIT command additionally aborts the current frame and would normal-
ly be given to the channel before clearing ENT. The command does not clear ENT auto-
matically. In a similar manner, to restart transmission, the user should issue the
RESTART TRANSMIT command and then set ENT. The command register is described
in 4.3 Command Set. The specific actions taken with each command vary somewhat ac-
cording to protocol and are discussed in each protocol section.
15
00 = HDLC
01 = Asynchronous (UART and DDCMP)
10 = Synchronous DDCMP and V.110
11 = BISYNC and Promiscuous Transparent
tools are 1) the ready bit in the transmit buffer descriptor, 2) the
ENT bit, 3) the STOP TRANSMIT command, 4) the RESTART
TRANSMIT command, and 5) the FRZ bit in the SCM (UART
mode only).
The DSR register has no relationship to the RS-232 signal “data
set ready,” which is also abbreviated DSR.
SYN2
MC68302 USER’S MANUAL
NOTE
8
7
Communications Processor (CP)
SYN1
4-31
0