MC68HC812A4 Datasheet, PDF (251/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Serial Communications Interface Module (SCI)
Register Descriptions and Reset Initialization
RSRC — Receiver Source Bit
When LOOPS = 1, the RSRC bit determines the internal feedback
path for the receiver.
1 = Receiver input connected to TXD pin
0 = Receiver input internally connected to transmitter output
Table 14-7. Loop Mode Functions
LOOPS
RSRC _DDRSx⁽¹⁾ WOMS
Function of TXD Pin
0
X
X
X
Normal operation
1
0
0
X
Loop mode; transmitter output connected to receiver input
TXD pin disconnected
1
0
1
0
Loop mode; transmitter output connected to receiver input
TXD is CMOS output
1
0
1
1
Loop mode; transmitter output connected to receiver input
TXD is open-drain output
1
1
0
x
Single-wire mode; transmitter output disconnected
TXD is high-impedance receiver input
1
1
1
0
Single-wire mode; TXD pin connected to receiver input
1
1
1
1
Single wire mode; TXD pin connected to receiver input
TXD is open-drain for receiving and transmitting
1. DDRSx means the data direction bit of the TXD pin.
M — Mode Bit
M determines whether data characters are eight or nine bits long.
1 = One start bit, nine data bits, one stop bit
0 = One start bit, eight data bits, one stop bit
WAKE — Wakeup Bit
WAKE determines which condition wakes up the SCI: a logic 1
(address mark) in the most significant bit position of a received data
character or an idle condition on the RXD pin.
1 = Address mark wakeup
0 = Idle line wakeup
Advance Information
MOTOROLA
Serial Communications Interface Module (SCI)
MC68HC812A4 — Rev. 3.0
251