HD-6402_05 Datasheet, PDF (4/7 Pages) Intersil Corporation – CMOS Universal Asynchronous Receiver Transmitter (UART)

HD-6402
HD-6402
Transmitter Operation
The transmitter section accepts parallel data, formats the data
and transmits the data in serial form on the Transmitter
Register Output (TRO) terminal (See serial data format). Data
is loaded from the inputs TBR1-TBR8 into the Transmitter
Buffer Register by applying a logic low on the Transmitter
Buffer Register Load (TBRL) input (A). Valid data must be
present at least t_set prior to and t_hold following the rising edge
of TBRL. If words less than 8 bits are used, only the least
significant bits are transmitted. The character is right justified,
so the least significant bit corresponds to TBR1 (B).
1
TBRL
TBRE
TRE
0 TO 1 CLOCK
The rising edge of TBRL clears Transmitter Buffer Register
Empty (TBRE). 0 to 1 Clock cycles later, data is transferred
to the transmitter register, the Transmitter Register Empty
(TRE) pin goes to a low state, TBRE is set high and serial
data information is transmitted. The output data is clocked by
Transmitter Register Clock (TRC) at a clock rate 16 times
the data rate. A second low level pulse on TBRL loads data
into the Transmitter Buffer Register (C). Data transfer to the
transmitter register is delayed until transmission of the cur-
rent data is complete (D). Data is automatically transferred to
the transmitter register and transmission of that character
begins one clock cycle later.
1/2 CLOCK
TRO
DATA
A
B
C
D ^{END OF LAST STOP BIT}
FIGURE 1. TRANSMITTER TIMING (NOT TO SCALE)
Receiver Operation
Data is received in serial form at the Receiver Register Input
(RRI). When no data is being received, RRI must remain
high. The data is clocked through the Receiver Register
Clock (RRC). The clock rate is 16 times the data rate. A low
level on Data Received Reset (DRR) clears the Data
Receiver (DR) line (A). During the first stop bit data is
transferred from the Receiver Register to the Receiver
Buffer Register (RBR) (B). 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 Overrun Error (OE) indicates overruns. An
overrun occurs when DR has not been cleared before the
present character was transferred to the RBR. One clock
cycle later DR is reset to a logic high, and Framing Error
(FE) is evaluated (C). A logic high on FE indicates an invalid
stop bit was received, a framing error. A logic high on Parity
Error (PE) indicates a parity error.
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