SC26C92A1A NXP Semiconductors, SC26C92A1A Datasheet - Page 12

• 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
the value in CTU and CTL and then restarted on the next C/T clock.
If the C/T is allowed to end the count before a new character has
been received, the counter ready bit, ISR[3], will be set. If IMR[3] is
set, this will generate an interrupt. Receiving a character after the
C/T has timed out will clear the counter ready bit, ISR[3], and the
interrupt. Invoking the ‘Set Timeout Mode On’ command, CRx = ‘Ax’,
will also clear the counter ready bit and stop the counter until the
next character is received.
Time Out Mode Caution
When operating in the special time out mode, it is possible to
generate what appears to be a “false interrupt”, i.e., an interrupt
without a cause. This may result when a time-out interrupt occurs
and then, BEFORE the interrupt is serviced, another character is
received, i.e., the data stream has started again. (The interrupt
latency is longer than the pause in the data stream.) In this case,
when a new character has been receiver, the counter/timer will be
restarted by the receiver, thereby withdrawing its interrupt. If, at this
time, the interrupt service begins for the previously seen interrupt, a
read of the ISR will show the “Counter Ready” bit not set. If nothing
else is interrupting, this read of the ISR will return a x’00 character.
The CTS, RTS, CTS Enable Tx signals
CTS (Clear To Send) is usually meant to be a signal to the transmit-
ter meaning that it may transmit data to the receiver. The CTS input
is on pin IP0 or IP1 for the transmitter. The CTS signal is active low;
thus, it is called CTSN. RTS is usually meant to be a signal from the
receiver indicating that the receiver is ready to receive data. It is
also active low and is, thus, called RTSN. RTSN is on pin OP0 or
OP1. A receiver’s RTS output will usually be connected to the CTS
input of the associated transmitter. Therefore, one could say that
RTS and CTS are different ends of the same wire!
MR2(4) is the bit that allows the transmitter to be controlled by the
CTS pin ( IP0 or IP1). When this bit is set to one AND the CTS
input is driven high, the transmitter will stop sending data at the end
of the present character being serialized. It is usually the RTS out-
put of the receiver that will be connected to the transmitter’s CTS
input. The receiver will set RTS high when the receiver FIFO is full
AND the start bit of the ninth character is sensed. Transmission
then stops with nine valid characters in the receiver. When MR2(4)
is set to one, CTSN must be at zero for the transmitter to operate. If
MR2(4) is set to zero, the IP0 or IP1 pin will have no effect on the
operation of the transmitter.
MR1(7) is the bit that allows the receiver to control OP0 or OP1.
When OP0 or OP1 is controlled by the receiver, the meaning of that
pin will be RTS. However, a point of confusion arises in that these
pins may also be controlled by the transmitter. When the transmit-
ter is controlling them the meaning is not RTS at all. It is, rather, that
the transmitter has finished sending its last data byte.
Programming the OP0 or OP1 pin to be controlled by the receiver
and the transmitter at the same time is allowed, but would usually be
incompatible.
RTS can also be controlled by the commands 1000 and 1001 in the
command register. RTS is expressed at the OP0 or OP1 pin which
is still an output port. Therefore, the state of OP0 or OP1 should be
set low (either by commands of the CR register or by writing to the
SOPR or ROPR (Set or Reset Output Port Registers) for the receiv-
er to generate the proper RTS signal. The logic at the output is
basically a NAND of the bit in OPR(0) or OPR(1) register and the
RTS signal as generated by the receiver. When the RTS flow con-
trol is selected via the MR1(7) bit the state of the OPR(0) or OPR(1)
register is not changed. Terminating the use of “Flow Control” (via
2000 Jan 31
Dual universal asynchronous receiver/transmitter (DUART)
12
the MR registers) will return the OP pins pin to the control of the
OPR register.
Multidrop Mode (9-bit or Wake-Up)
The DUART is equipped with a wake up mode for multidrop
applications. This mode is selected by programming bits MR1A[4:3]
or MR1B[4:3] to ‘11’ for Channels A and B, respectively. In this
mode of operation, a ‘master’ station transmits an address character
followed by data characters for the addressed ‘slave’ station. The
slave stations, with receivers that are normally disabled, examine
the received data stream and ‘wakeup’ the CPU (by setting RxRDY)
only upon receipt of an address character. The CPU compares the
received address to its station address and enables the receiver if it
wishes to receive the subsequent data characters. Upon receipt of
another address character, the CPU may disable the receiver to
initiate the process again.
A transmitted character consists of a start bit, the programmed
number of data bits, and Address/Data (A/D) bit, and the
programmed number of stop bits. The polarity of the transmitted
A/D bit is selected by the CPU by programming bit
MR1A[2]/MR1B[2]. MR1A[2]/MR1B[2] = 0 transmits a zero in the
A/D bit position, which identifies the corresponding data bits as data
while MR1A[2]/MR1B[2] = 1 transmits a one in the A/D bit position,
which identifies the corresponding data bits as an address. The
CPU should program the mode register prior to loading the
corresponding data bits into the TxFIFO.
In this mode, the receiver continuously looks at the received data
stream, whether it is enabled or disabled. If disabled, it sets the
RxRDY status bit and loads the character into the RxFIFO if the
received A/D bit is a one (address tag), but discards the received
character if the received A/D bit is a zero (data tag). If enabled, all
received characters are transferred to the CPU via the RxFIFO. In
either case, the data bits are loaded into the data FIFO while the
A/D bit is loaded into the status FIFO position normally used for
parity error (SRA[5] or SRB[5]). Framing error, overrun error, and
break detect operate normally whether or not the receive is enabled.
PROGRAMMING
The operation of the DUART is programmed by writing control words
into the appropriate registers. Operational feedback is provided via
status registers which can be read by the CPU. The addressing of
the registers is described in Table 1.
The contents of certain control registers are initialized to zero on
RESET. Care should be exercised if the contents of a register are
changed during operation, since certain changes may cause
operational problems.
For example, changing the number of bits per character while the
transmitter is active may cause the transmission of an incorrect
character. In general, the contents of the MR, the CSR, and the
OPCR should only be changed while the receiver(s) and
transmitter(s) are not enabled, and certain changes to the ACR
should only be made while the C/T is stopped.
Each channel has 3 mode registers (MR0, 1, 2) which control the
basic configuration of the channel. Access to these registers is
controlled by independent MR address pointers. These pointers are
set to 0 or 1 by MR control commands in the command register
“Miscellaneous Commands”. Each time the MR registers are
accessed the MR pointer increments, stopping at MR2. It remains
pointing to MR2 until set to 0 or 1 via the miscellaneous commands
of the command register. The pointer is set to 1 on reset for
compatibility with previous Philips Semiconductors UART software.
Product specification
SC26C92