MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 280

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

Signal Description
In PCM mode, L1SY1–L1SY0 are encoded signals used to create channels that can be in-
dependently routed to the SCCs.
In IDL/GCI modes, the SDS2–SDS1 outputs may be used to route the B1 and/or B2 chan-
nels to devices that do not support the IDL or GCI buses. This is configured in the serial in-
terface mode (SIMODE) and serial interface mask (SIMASK) registers.
CD1/L1SY1—Carrier Detect/Layer-1 Sync
CTS1/L1GR—Clear to Send/Layer-1 Grant
5-16
This input is used as the NMSI1 carrier detect (CD) pin in NMSI mode, as a PCM sync
signal in PCM mode, and as an L1SYNC signal in IDL/GCI modes.
If the CD1 pin has changed for more than one receive clock cycle, the IMP asserts the
appropriate bit in the SCC1 event register. If the SCC1 channel is programmed not to sup-
port CD1 automatically (in the SCC1 mode register), then this pin may be used as an ex-
ternal interrupt source. The current value of CD1 may be read in the SCCS1 register. See
4.5.8.3 SCC Status Register (SCCs) for details. CD1 may also be used as an external
sync in NMSI mode.
This input is the NMSI1 CTS signal in the NMSI mode or the grant signal in the IDL/GCI
mode. If this pin is not used as a grant signal in GCI mode, it should be connected to V
If the CTS1 pin has changed for more than one transmit clock cycle, the IMP asserts the
appropriate bit in the SCC1 event register and optionally aborts the transmission of that
frame.
When using SCC1 in the NMSI mode with the internal baud rate
generator operating, the TCLK1 and RCLK1 pins will always out-
put the baud rate generator clock unless disabled in the CKCR
register. Thus, if a dynamic selection between an internal and
external clock source is required in an application, the clock pins
should be disabled first in the CKCR register before switching
the TCLK1 and RCLK1 lines. On SCC2 and SCC3, contention
may be avoided by disabling the clock line outputs in the PACNT
register.
NOTE: CH-1, 2, and 3 are connected to the SCCs as determined in the
L1SY1
0
0
1
1
SIMODE register.
Table 5-8. PCM Mode Signals
L1SY0
0
1
0
1
MC68302 USER’S MANUAL
L1TXD is Three-Stated, L1RXD is Ignored
CH-1
CH-2
CH-3
Data (L1RXD, L1TXD) is Routed to SCC
NOTE
MOTOROLA
DD
.