TA550C datasheet(32/39 Pages) TI

32 / 39 page

TL16C550C, TL16C550CI

ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH AUTOFLOW CONTROL

SLLS177F – MARCH 1994 – REVISED MARCH 2001

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

modem status register (MSR) (continued)

D Bit 3: This bit is the change in data carrier detect (∆DCD) indicator. ∆DCD indicates that the DCD input to

the chip has changed state since the last time it was read by the CPU. When

∆DCD is set and the modem

status interrupt is enabled, a modem status interrupt is generated.

D Bit 4: This bit is the complement of the clear-to-send (CTS) input. When the ACE is in the diagnostic test

mode (LOOP [MCR4] = 1), this bit is equal to the MCR bit 1 (RTS).

D Bit 5: This bit is the complement of the data set ready (DSR) input. When the ACE is in the diagnostic test

mode (LOOP [MCR4] = 1), this bit is equal to the MCR bit 0 (DTR).

D Bit 6: This bit is the complement of the ring indicator (RI) input. When the ACE is in the diagnostic test mode

(LOOP [MCR4] = 1), this bit is equal to the MCR bit 2 (OUT1).

D Bit 7: This bit is the complement of the data carrier detect (DCD) input. When the ACE is in the diagnostic

test mode (LOOP [MCR4] = 1), this bit is equal to the MCR bit 3 (OUT2).

programmable baud generator

The ACE contains a programmable baud generator that takes a clock input in the range between dc and 16 MHz

and divides it by a divisor in the range between 1 and (216 –1). The output frequency of the baud generator is

sixteen times (16

×) the baud rate. The formula for the divisor is:

divisor = XIN 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.

Tables 9 and 10 illustrate the use of the baud generator with crystal frequencies of 1.8432 MHz and 3.072 MHz

respectively. For baud rates of 38.4 kbits/s and below, the error obtained is very small. The accuracy of the

selected baud rate is dependent on the selected crystal frequency (refer to Figure 23 for examples of typical

clock circuits).

TA550C Datasheet(PDF) 32 Page - Texas Instruments