Motorola DSP56301 - Manual (Page 253)

SCI Programming Model
Serial Communication Interface (SCI) 8 -17
8.6.2 SCI Status Register (SSR)
The SSR is a read-only register that indicates the status of the SCI.
23 22 21 20 19 18 17 16
15 14 13 12 11 10 9 8
7 6 5 4 3 2 1 0
R8 FE PE OR IDLE RDRF TDRE TRNE
—Reserved bit; read as 0; write to 0 for future compatibility.
Table 8-3. SCI Status Register
Table 8-4. SCI Status Register (SSR) Bit Definitions
Bit
Number
Bit Name
Reset
Value
Description
23–8 0 Reserved. Write to 0 for future compatibility.
7 R8 0 Received Bit 8
In 11-bit Asynchronous Multidrop mode, the R8 bit indicates whether the
received byte is an address or data. R8 is set for addresses and is cleared for
data. R8 is not affected by reads of the SRX or SCI status register. A hardware
RESET signal, a software RESET instruction, an SCI individual reset, or a STOP
instruction clears R8.
6 FE 0 Framing Error Flag
In Asynchronous mode, FE is set when no stop bit is detected in the data string
received. FE and RDRE are set simultaneously when the received word is
transferred to the SRX. However, the FE flag inhibits further transfer of data into
the SRX until it is cleared. FE is cleared when the SCI status register is read
followed by a read of the SRX. A hardware RESET signal, a software RESET
instruction, an SCI individual reset, or a STOP instruction clears FE. In 8-bit
Synchronous mode, FE is always cleared. If the byte received causes both
framing and overrun errors, the SCI receiver recognizes only the overrun error.
5 PE 0 Parity Error
In 11-bit Asynchronous modes, PE is set when an incorrect parity bit is detected
in the received character. PE and RDRF are set simultaneously when the
received word is transferred to the SRX. If PE is set, further data transfer into the
SRX is not inhibited. PE is cleared when the SCI status register is read, followed
by a read of SRX. A hardware RESET signal, a software RESET instruction, an
SCI individual reset, or a STOP instruction also clears PE. In 10-bit
Asynchronous mode, 11-bit multidrop mode, and 8-bit Synchronous mode, the
PE bit is always cleared since there is no parity bit in these modes. If the byte
received causes both parity and overrun errors, the SCI receiver recognizes only
the overrun error.