CDP6402CD HARRIS [Harris Corporation], CDP6402CD Datasheet - Page 5

• Manufacturer Part Number: CDP6402CD
• Description: CMOS Universal Asynchronous Receiver/Transmitter (UART)
• Manufacturer: HARRIS [Harris Corporation]

Description of Operation
Initialization and Controls
A positive pulse on the MASTER RESET (MR) input resets
the control, status, and receiver buffer registers, and sets the
serial output (TRO) High. Timing is generated from the clock
inputs RRC and TRC at a frequency equal to 16 times the
serial data bit rate. The RRC and TRC inputs may be driven
by a common clock, or may be driven independently by two
different clocks. The CONTROL REGISTER LOAD (CRL)
input is strobed to load control bits for PARITY INHIBIT (PI),
EVEN PARITY ENABLE (EPE), STOP BIT SELECTS (SBS),
and CHARACTER LENGTH SELECTS (CLS1 and CLS2).
These inputs may be hand wired to V
V
for receiver and/or transmitter operations.
Transmitter Operation
The transmitter section accepts parallel data, formats it, and
transmits it in serial form (Figure 2) on the TRO terminal.
Transmitter timing is shown in Figure 3. (A) Data is loaded
into the transmitter buffer register from the inputs TBR1
through TBR8 by a logic low on the TBRL input. Valid data
must be present at least t
rising edge of TBRL. If words less than 8-bits are used, only
the least significant bits are used. The character is right justi-
fied into the least significant bit, TBR1. (B) The rising edge of
TBRL clears TBRE. 1/2 to 11/2 cycles later, depending on
when the TBRL pulse occurs with respect to TRC, data is
transferred to the transmitter register and TRE is cleared.
TBRE is set to a logic High one cycle after that.
Output data is clocked by TRC. The clock rate is 16 times
the data rate. (C) A second pulse on TBRL loads data into
the transmitter buffer register. Data transfer to the transmitter
register is delayed until transmission of the current character
is complete. (D) Data is automatically transferred to the
transmitter register and transmission of that character
begins.
TBRL
TBRE
START
†
TRO
DD
TRE
IF ENABLED
BIT
. When the initialization is completed, the UART is ready
FIGURE 3. TRANSMITTER TIMING WAVEFORMS
LSB
A
FIGURE 2. SERIAL DATA FORMAT
1/2 TO 1-1/2 CYCLES
B
5 - 8 DATA BITS
1 TO 2 CYCLES
DT
1-1/2 TO 2-1/2 CYCLES
prior to, and t
C
SS
DATA
MSB
or V
TD
DD
D
†
CDP6402, CDP6402C
2 STOP BITS
following, the
1, 1-1/2 OR
with CRL to
PARITY
1/2
CLOCK
END OF
LAST
STOP BIT
5-78
Receiver Operation
Data is received in serial form at the RRl input. When no
data is being received, RRI input must remain high. The data
is clocked through the RRC. The clock rate is 16 times the
data rate. Receiver timing is shown in Figure 4.
(A) A low level on DRR clears the DR line. (B) During the first
stop bit data is transferred from the receiver register to the
RB Register. If the word is less than 8 bits, the unused most
significant bits will be a logic low. The output character is
right justified to the least significant bit RBR1. A logic high on
OE indicates overruns. An overrun occurs when DR has not
been cleared before the present character was transferred to
the RBR. (C) 1/2 clock cycle later DR is set to a logic high
and FE is evaluated. A logic high on FE indicates an invalid
stop bit was received. A logic high on PE indicates a parity
error.
Start Bit Detection
The receiver uses a 16X clock for timing (Figure 5). The start
bit could have occurred as much as one clock cycle before it
was detected, as indicated by the shaded portion. The cen-
ter of the start bit is defined as clock count 7 1/2. If the
receiver clock is a symmetrical square wave, the center of
the start bit will be located within 1/2 clock cycle 1/32 bit or
at 9 clocks into the first stop bit.
RBRI-8, OE
DRR
FE, PE
CLOCK
RRI
3.125%. The receiver begins searching for the next start bit
DR
INPUT
RRI
BEGINNING OF FIRST STOP BIT
FIGURE 4. RECEIVER TIMING WAVEFORMS
FIGURE 5. START BIT TIMING WAVEFORMS
A
A
8 1/2 CLOCK
7 1/2 CLOCK
CYCLES
CYCLES
START
B
DEFINED CENTER
OF START BIT
COUNT 7 1/2
8 1/2 TO 9 1/2
CLOCK CYCLES
C
1/2 CLOCK
CYCLES