SCC68692C1F40 PHILIPS [NXP Semiconductors], SCC68692C1F40 Datasheet - Page 19

• Manufacturer Part Number: SCC68692C1F40
• Description: Dual asynchronous receiver/transmitter DUART
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
ISR[7] – Input Port Change Status
This bit is a ‘1’ when a change-of-state has occurred at the IP0, IP1,
IP2, or IP3 inputs and that event has been selected to cause an
interrupt by the programming of ACR[3:0]. The bit is cleared when
the CPU reads the IPCR.
ISR[6] – Channel B Change In Break
This bit, when set, indicates that the Channel B receiver has detected
the beginning or the end of a received break. It is reset when the
CPU issues a Channel B ‘reset break change interrupt’ command.
ISR[5] – Channel B Receiver Ready or FIFO Full
The function of this bit is programmed by MR1B[6]. If programmed
as receiver ready, it indicates that a character has been received in
Channel B 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 RHR. If after this
read there are more characters still in the FIFO the bit will be set
again after the FIFO is ‘popped’. If programmed as FIFO full, it is
set when a character is transferred from the receive holding register
to the receive FIFO and the transfer caused the Channel B FIFO to
become full; i.e., all three FIFO positions are occupied. It is reset
when the CPU reads the RHR. If a character is waiting in the
receive shift register because the FIFO is full, the bit will be set
again when the waiting character is loaded into the FIFO.
ISR[4] – Channel B Transmitter Ready
This bit is a duplicate of TxRDYB (SRB[2]).
ISR[3] – Counter Ready.
In the counter mode, this bit is set when the counter reaches
terminal count and is reset when the counter is stopped by a stop
counter command.
In the timer mode, this bit is set once each cycle of the generated
square wave (every other time that the counter/timer reaches zero
count). The bit is reset by a stop counter command. The command,
however, does not stop the counter/timer.
ISR[2] – Channel A Change in Break
This bit, when set, indicates that the Channel A receiver has
detected the beginning or the end of a received break. It is reset
when the CPU issues a Channel A ‘reset break change interrupt’
command.
ISR[1] – Channel A Receiver Ready Or FIFO Full
The function of this bit is programmed by MR1A[6]. If programmed
as receiver ready, it indicates that a character has been received in
Channel A 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 RHR. If after this
read there are more characters still in the FIFO the bit will be set
again after the FIFO is ‘popped’. If programmed as FIFO full, it is
set when a character is transferred from the receive holding register
to the receive FIFO and the transfer caused the Channel A FIFO to
become full; i.e., all three FIFO positions are occupied. It is reset
when the CPU reads the RHR. If a character is waiting in the
receive shift register because the FIFO is full, the bit will be set
again when the ISR[0] and IMR waiting character is loaded into the
FIFO.
ISR[0] – Channel A Transmitter Ready
This bit is a duplicate of TxRDYA (SRA[2]).
1998 Sep 04
Dual asynchronous receiver/transmitter (DUART)
19
continues counting past the terminal count until stopped by the CPU.
example. One can only program integer numbers in a digital divider.
IMR – Interrupt Mask Register
The programming of this register selects which bits in the ISR
causes an interrupt output. If a bit in the ISR is a ‘1’ and the
corresponding bit in the IMR is also a ‘1’ the INTRN output will be
asserted. If the corresponding bit in the IMR is a zero, the state of
the bit in the ISR has no effect on the INTRN output. Note that the
IMR does not mask the programmable interrupt outputs OP3–OP7
or the reading of the ISR.
CTUR and CTLR – Counter/Timer Registers
The CTUR and CTLR hold the eight MSBs and eight LSBs,
respectively, of the value to be used by the counter/timer in either
the counter or timer modes of operation. The minimum value which
may be loaded into the CTUR/CTLR registers is H‘0002’. Note that
these registers are write-only and cannot be read by the CPU.
In the timer (programmable divider) mode, the C/T generates a
square wave with a period of twice the value (in clock periods) of the
CTUR and CTLR. The waveform so generated is often used for a
data clock. The formula for calculating the divisor n to load to the
CTUR and CTLR for a particular 1X data clock is shown below:
Often this division will result in a non-integer number; 26.3, for
Therefore, 26 would be chosen. This gives a baud rate error of
0.3/26.3 which is 1.14%; well within the ability asynchronous mode
of operation.
If the value in CTUR and CTLR is changed, the current half-period
will not be affected, but subsequent half periods will be. The C/T will
not be running until it receives an initial ‘Start Counter’ command
(read at address A3–A0 = 1110). After this, while in timer mode, the
C/T will run continuously. Receipt of a start counter command (read
with A3–A0 = 1110) causes the counter to terminate the current
timing cycle and to begin a new cycle using the values in CTUR and
CTLR.
The counter ready status bit (ISR[3]) is set once each cycle of the
square wave. The bit is reset by a stop counter command (read
with A3–A0 = H‘F’). The command however, does not stop the C/T.
The generated square wave is output on OP3 if it is programmed
to be the C/T output.
In the counter mode, the C/T counts down the number of pulses
loaded into CTUR and CTLR by the CPU. Counting begins upon
receipt of a start counter command. Upon reaching terminal count
H‘0000’, the counter ready interrupt bit (ISR[3]) is set. The counter
If OP3 is programmed to be the output of the C/T, the output
remains High until terminal count is reached, at which time it goes
Low. The output returns to the High state and ISR[3] is cleared
when the counter is stopped by a stop counter command. The
CPU may change the values of CTUR and CTLR at any time, but
the new count becomes effective only on the next start counter
commands. If new values have not been loaded, the previous count
values are preserved and used for the next count cycle
In the counter mode, the current value of the upper and lower 8 bits
of the counter (CTU, CTL) may be read by the CPU. It is
recommended that the counter be stopped when reading to prevent
n +
16 x 2 x baud rate desired
counter clock frequency
SCC68692
Product specification