Philips Semiconductors Product data sheet
SC28L202Dual UART
2005 Nov 01
43
SR Status Register
Bit 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
SR A
SR B
RECEIVED
BREAK*
FRAMING
ERROR*
PARITY
ERROR*
OVERRUN
ERROR
TxEMT TxRDY FFULL RxRDY
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
NOTE: *These status bits are appended to the corresponding data character in the receive FIFO. A read of the status provides these bits
(7:5) from the top of the FIFO together with bits (4:0). These bits are cleared by a ‘reset error status’ command. In character mode they are
discarded when the corresponding data character is read from the FIFO. In block error mode, the error–reset command (command 4x or
receiver reset) must used to clear block error conditions
SR A[7] – Received Break
Channel A Received Break. This bit indicates that an all zero
character of the programmed length has been received without a
stop bit. Only a single FIFO position is occupied when a break is
received: further entries to the FIFO are inhibited until the RxD A line
returns to the marking state for at least one–half a bit time two
successive edges of the internal or external 1X clock. This will
usually require a high time of one X1 clock period or 3 X1 edges
since the clock of the controller is not synchronous to the X1 clock.
When this bit is set, the Channel A ‘change in break’ bit in the ISR
(ISR[2]) is set. ISR[2] is also set when the end of the break
condition, as defined above, is detected.
The break detect circuitry can detect breaks that originate in the
middle of a received character. However, if a break begins in the
middle of a character, it must persist until at least the end of the next
character time in order for it to be detected.
This bit is reset by command 4 (0100) written to the command
register or by receiver reset.
SR A[6] – Channel A Framing Error
This bit, when set, indicates that a stop bit was not detected when
the corresponding data character in the FIFO was received. The
stop bit check is made in the middle of the first stop bit position.
SR A[5] – Channel A Parity Error
This bit is set when the ‘with parity’ or ‘force parity’ mode is
programmed and the corresponding character in the FIFO was
received with incorrect parity.
In the special multi–drop mode the parity error bit stores the receive
A/D (Address/Data) bit.
SR A[4] – Channel A Overrun Error
This bit, when set, indicates that one or more characters in the
received data stream have been lost. It is set upon receipt of a new
character when the FIFO is full and a character is already in the
receive shift register waiting for an empty FIFO position. When this
occurs, the character in the receive shift register (and its break
detect, parity error and framing error status, if any) is lost.
This bit is cleared by a ‘reset error status’ command.
SR A[3] – Channel A Transmitter Empty (TxEMT A)
This bit will be set when the transmitter under runs, i.e., both the
TxEMT and TxRDY bits are set. This bit and TxRDY are set when
the transmitter is first enabled and at any time it is re–enabled after
either (a) reset, or (b) the transmitter has assumed the disabled
state. It is always set after transmission of the last stop bit of a
character if no character is in the THR awaiting transmission.
It is reset when the THR is loaded by the CPU, a pending
transmitter disable is executed, the transmitter is reset, or the
transmitter is disabled while in the under run condition.
SR A[2] – Channel A Transmitter Ready (TxRDY A)
This bit, when set, indicates that the transmit FIFO is not full and
ready to be loaded with another character. This bit is cleared when
the transmit FIFO is loaded by the CPU and there are (after this
load) no more empty locations in the FIFO. It is set when a
character is transferred to the transmit shift register. TxRDY A is
reset when the transmitter is disabled and is set when the
transmitter is first enabled. Characters loaded to the TxFIFO while
this bit is 0 will be lost. This bit has different meaning from ISR[0].
SR A[1] – Channel A FIFO Full (FFULL A)
This bit is set when a character is transferred from the receive shift
register to the receive FIFO and the transfer causes the FIFO to
become full, i.e., all eight FIFO positions are occupied. It is reset
when the CPU reads the receive FIFO. If a character is waiting in
the receive shift register because the FIFO is full, FFULL A will not
be reset when the CPU reads the receive FIFO. This bit has
different meaning from ISR1 when MR1 6 is programmed to a ‘1’.
SR A[0] – Channel A Receiver Ready (RxRDY A)
This bit indicates that a character has been received and is waiting
in the FIFO to be read by the CPU. It is set when the character is
transferred from the receive shift register to the FIFO and reset
when the CPU reads the receive FIFO, only if (after this read) there
are no more characters in the FIFO.
SR B – Channel B Status Register
The bit definitions for this register are identical to the bit definitions
for SR A, except that all status applies to the Channel B receiver
and transmitter and the corresponding inputs and outputs.
