MC68HC05B4 Datasheet, PDF (82/298 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

6.11
SCI registers
The SCI system is configured and controlled by five registers: SCDR, SCCR1, SCCR2, SCSR,
and BAUD.
6.11.1 Serial communications data register (SCDR)
SCI data (SCDR)
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$0011
0000 0000
The SCDR is controlled by the internal R/W signal and performs two functions in the SCI. It acts
as the receive data register (RDR) when it is read and as the transmit data register (TDR) when it
6
is written. Figure 6-1 shows this register as two separate registers, RDR and TDR. The RDR
provides the interface from the receive shift register to the internal data bus and the TDR provides
the parallel interface from the internal data bus to the transmit shift register.
The receive data register is a read-only register containing the last byte of data received from the
shift register for the internal data bus. The RDR full bit (RDRF) in the serial communications status
register is set to indicate that a byte has been transferred from the input serial shift register to the
SCDR. The transfer is synchronized with the receiver bit rate clock (from the receiver control) as
shown in Figure 6-1. All data is received with the least significant bit first.
The transmit data register (TDR) is a write-only register containing the next byte of data to be
applied to the transmit shift register from the internal data bus. As long as the transmitter is
enabled, data stored in the SCDR is transferred to the transmit shift register (after the current byte
in the shift register has been transmitted).
The transfer is synchronized with the transmitter bit rate clock (from the transmitter control) as
shown in Figure 6-1. All data is received with the least significant bit first.
6.11.2 Serial communications control register 1 (SCCR1)
SCI control 1 (SCCR1)
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$000E R8 T8
M WAKE CPOL CPHA LBCL Undefined
The SCI control register 1 (SCCR1) contains control bits related to the nine data bit character
format, the receiver wake-up feature and the options to output the transmitter clocks for
synchronous transmissions.
MOTOROLA
6-10
SERIAL COMMUNICATIONS INTERFACE
TPG
MC68HC05B6
Rev. 4