SC26C92A1A NXP Semiconductors, SC26C92A1A Datasheet - Page 10

• Manufacturer Part Number: SC26C92A1A
• Description: IC, UART, DUAL, SMD, 26C92, PLCC44
• Manufacturer: NXP Semiconductors

Specifications of SC26C92A1A

• No. Of Channels: 2
• Supply Voltage Range: 4.5V To 5.5V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: PLCC
• No. Of Pins: 44
• Svhc: No SVHC (18-Jun-2010)
• Operating Temperature: RoHS Compliant
• Data Rate: 230.4Kilobaud
• Uart Features: Parity, Framing, & Overrun Error Detection, Start-End Break Interrupt/Status
• Rohs Compliant: Yes

Philips Semiconductors
This feature may be used automatically “turnaround” a transceiver
when operating in a simplex system.
Transmitter Disable Note (W.R.T. Turnaround)
When the TxEMT bit is set the sequence of instructions: enable
transmitter — load transmit holding register — disable transmitter
will often result in nothing being sent. In the condition of the TxEMT
being set do not issue the disable until the TxRDY bit goes active
again after the character is loaded to the TxFIFO. The data is not
sent if the time between the end of loading the transmit holding
register and the disable command is less that 3/16 bit time in the
16x mode. One bit time in the 1x mode.
This is sometimes the condition when the RS485 automatic “turn-
around” is enabled . It will also occur when only one character is to
be sent and it is desired to disable the transmitter immediately after
the character is loaded.
In general, when it is desired to disable the transmitter before the
last character is sent AND the TxEMT bit is set in the status register
be sure the TxRDY bit is active immediately before issuing the
transmitter disable instruction. (TxEMT is always set if the transmit-
ter has underrun or has just been enabled), TxRDY sets at the end
of the “start bit” time. It is during the start bit that the data in the
transmit holding register is transferred to the transmit shift register.
Transmitter Flow control
The transmitter may be controlled by the CTSN input when enabled
by MR2(4). The CTSN input would be connected to RTSN output of
the receiver to which it is communicating. See further description in
the MR 1 and MR2 register descriptions.
Receiver
The SC26C92 is conditioned to receive data when enabled through
the command register. The receiver looks for a High-to-Low
(mark-to-space) transition of the start bit on the RxD input pin. If a
transition is detected, the state of the RxD pin is sampled each 16X
clock for 7-1/2 clocks (16X clock mode) or at the next rising edge of
the bit time clock (1X clock mode). If RxD is sampled High, the start
bit is invalid and the search for a valid start bit begins again. If RxD
is still Low, a valid start bit is assumed and the receiver continues to
sample the input at one bit time intervals at the theoretical center of
the bit, until the proper number of data bits and parity bit (if any)
have been assembled, and one stop bit has been detected. The
least significant bit is received first. The data is then transferred to
the Receive FIFO and the RxRDY bit in the SR is set to a 1. This
condition can be programmed to generate an interrupt at OP4 or
OP5 and INTRN. If the character length is less than 8 bits, the most
significant unused bits in the RxFIFO are set to zero.
After the stop bit is detected, the receiver will immediately look for
the next start bit. However, if a non-zero character was received
without a stop bit (framing error) and RxD remains Low for one half
of the bit period after the stop bit was sampled, then the receiver
operates as if a new start bit transition had been detected at that
point (one-half bit time after the stop bit was sampled).
The parity error, framing error, and overrun error (if any) are strobed
into the SR at the received character boundary, before the RxRDY
status bit is set. If a break condition is detected (RxD is Low for the
entire character including the stop bit), a character consisting of all
zeros will be loaded into the RxFIFO and the received break bit in
the SR is set to 1. The RxD input must return to high for two (2)
clock edges of the X1 crystal clock for the receiver to recognize the
end of the break condition and begin the search for a start bit. This
will usually require a high time of one X1 clock period or 3 X1
2000 Jan 31
Dual universal asynchronous receiver/transmitter (DUART)
10
edges since the clock of the controller is not synchronous to
the X1 clock.
Receiver FIFO
The RxFIFO consists of a First-In-First-Out (FIFO) stack with a
capacity of eight characters. Data is loaded from the receive shift
register into the topmost empty position of the FIFO. The RxRDY bit
in the status register is set whenever one or more characters are
available to be read, and a FFULL status bit is set if all eight stack
positions are filled with data. Either of these bits can be selected to
cause an interrupt. A read of the RxFIFO outputs the data at the top
of the FIFO. After the read cycle, the data FIFO and its associated
status bits (see below) are ‘popped’ thus emptying a FIFO position
for new data.
Receiver Status Bits
There are five (5) status bits that are evaluated with each byte (or
character) received: received break, framing error, parity error, over-
run error, and change of break. The first three are appended to
each byte and stored in the RxFIFO. The last two are not necessar-
ily related to the byte being received or a byte that is in the RxFIFO.
They are however developed by the receiver state machine.
The received break, framing error, parity error and overrun error (if
any) are strobed into the RxFIFO at the received character bound-
ary, before the RxRDY status bit is set. For character mode (see
below) status reporting the SR (Status Register) indicates the condi-
tion of these bits for the character that is the next to be read from the
FIFO
The ”received break” will always be associated with a zero byte in
the RxFIFO. It means that zero character was a break character
and not a zero data byte. The reception of a break condition will
always set the ”change of break” (see below) status bit in the Inter-
rupt Status Register (ISR). The Change of break condition is reset
by a reset error status command in the command register
Break Detection
If a break condition is detected (RxD is Low for the entire character
including the stop bit), a character consisting of all zeros will be
loaded into the RxFIFO and the received break bit in the SR is set to
1. The change of break bit also sets in the ISR The RxD input must
return to high for two (2) clock edges of the X1 crystal clock for the
receiver to recognize the end of the break condition and begin the
search for a start bit.
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.
Framing Error
A framing error occurs when a non–zero character whose parity bit
(if used) and stop; bit are zero. If RxD remains low for one half of
the bit period after the stop bit was sampled, then the receiver
operates as if the start bit of the next character had been detected.
The parity error indicates that the receiver–generated parity was not
the same as that sent by the transmitter.
The framing, parity and received break status bits are reset when
the associated data byte is read from the RxFIFO since these “error”
conditions are attached to the byte that has the error
Overrun Error
The overrun error occurs when the RxFIFO is full, the receiver shift
register is full, and another start bit is detected. At this moment the
receiver has 9 valid characters and the start bit of the 10
Product specification
SC26C92
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