Datasheet

TL16C750
ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH 64-BYTE FIFOs AND AUTOFLOW CONTROL
SLLS191C – JANUARY 1995 – REVISED DECEMBER 1997
6
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
autoflow control (continued)
Serial to
Parallel
Flow
Control
Parallel
to Serial
Flow
Control
Parallel
to Serial
Flow
Control
Serial to
Parallel
Flow
Control
XMT
FIFO
RCV
FIFO
ACE1 ACE2
D7–D0
D7–D0
SIN SOUT
RTS
CTS
SOUT SIN
CTS
RTS
XMT
FIFO
RCV
FIFO
Figure 1. Autoflow Control (auto-RTS and auto-CTS) Example
auto-RTS (see Figure 1)
Auto-RTS
data flow control originates in the receiver timing and control block (see functional block diagram)
and is linked to the programmed receiver FIFO trigger level. When the receiver FIFO level reaches a trigger level
of 1, 4, 8, or 14 in 16-byte mode or 1, 16, 32, or 56 in 64-byte mode, RTS
is deasserted. The sending ACE may
send an additional byte after the trigger level is reached (assuming the sending ACE has another byte to send)
because it may not recognize the deassertion of RTS
until after it has begun sending the additional byte. RTS
is automatically reasserted once the receiver FIFO is emptied by reading the receiver buffer register. The
reassertion signals the sending ACE to continue transmitting data.
auto-CTS
(see Figure 1)
The transmitter circuitry checks CTS
before sending the next data byte. When CTS is active, the transmitter
sends the next byte. To stop the transmitter from sending the following byte, CTS
must be released before the
middle of the last stop bit that is currently being sent. The auto-CTS
function reduces interrupts to the host
system. When flow control is enabled, the CTS
state changes and does not trigger host interrupts because the
device automatically controls its own transmitter. Without auto-CTS
, the transmitter sends any data present in
the transmit FIFO and a receiver overrun error can result.
enabling auto-RTS
and auto-CTS
The auto-RTS and auto-CTS modes of operation are activated by setting bit 5 of the modem control register
(MCR) to 1 (see Figure 2).
Start Bits 0–7 Start Bits 0–7 Start Bits 0–7
Stop Stop Stop
SOUT
CTS
NOTES: A. When CTS is low, the transmitter keeps sending serial data out.
B. When CTS
goes high before the middle of the last stop bit of the current byte, the transmitter finishes sending the current byte but
it does not send the next byte.
C. When CTS
goes from high to low, the transmitter begins sending data again.
Figure 2. CTS Functional Timing