TL16C451 Datasheet, PDF (22/23 Pages) Texas Instruments – ASYNCHRONOUS COMMUNICATIONS ELEMENTS

TL16C451, TL16C452
ASYNCHRONOUS COMMUNICATIONS ELEMENTS
SLLS053C – MAY 1989 – REVISED AUGUST 1999
PRINCIPLES OF OPERATION
programmable baud generator
The ACE contains a programmable baud generator that takes a clock input in the range between dc and 9 MHz
and divides it by a divisor in the range between 1 and (2^{16 –} 1). The output frequency of the baud generator is
sixteen times (16 ×) the baud rate. The formula for the divisor is:
divisor # = CLK frequency input ÷ (desired baud rate × 16)
Two 8-bit registers, called divisor latches, store the divisor in a 16-bit binary format. These divisor latches must
be loaded during initialization of the ACE in order to ensure desired operation of the baud generator. When either
of the divisor latches is loaded, a 16-bit baud counter is also loaded to prevent long counts on initial load. For
baud rates of 38.4 kilobits per second and below, the error obtained is very small. The accuracy of the selected
baud rate is dependent on the selected crystal frequency.
receiver buffer register (RBR)
The ACE receiver section consists of a receiver shift register and an RBR. Timing is supplied by the 16× receiver
clock (RCLK). Receiver section control is a function of the ACE line control register.
The ACE receiver shift register receives serial data from the serial input (SIN) terminal. The receiver shift
register then converts the data to a parallel form and loads it into the RBR. When a character is placed in the
RBR and the received data available interrupt is enabled, an interrupt is generated. This interrupt is cleared
when the data is read out of the RBR.
scratch register
The scratch register is an 8-bit register that is intended for programmer use as a scratchpad, in the sense that
it temporarily holds programmer data without affecting any other ACE operation.
transmitter holding register (THR)
The ACE transmitter section consists of a THR and a transmitter shift register. Timing is supplied by the baud
out (BAUDOUT) clock signal. Transmitter section control is a function of the ACE line control register.
The ACE THR receives data off of the internal data bus and, when the shift register is idle, moves it into the
transmitter shift register. The transmitter shift register serializes the data and outputs it at the serial output
(SOUT). When the THR is empty and the transmitter holding register empty (THRE) interrupt is enabled, an
interrupt is generated. This interrupt is cleared when a character is loaded into the register.
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