
Philips Semiconductors
SC16C750
Universal Asynchronous Receiver/Transmitter (UART) with 64-byte FIFO
Product data
Rev. 03 — 14 March 2003
11 of 45
9397 750 11203
Koninklijke Philips Electronics N.V. 2003. All rights reserved.
6.3 Hardware ow control
When automatic hardware ow control is enabled, the SC16C750 monitors the CTS
pin for a remote buffer overow indication and controls the RTS pin for local buffer
overows. Automatic hardware ow control is selected by setting EFR[6] (RTS) and
EFR[7] (CTS) to a logic 1. If CTS transitions from a logic 0 to a logic 1 indicating a
ow control request, the SC16C750 will suspend TX transmissions as soon as the
stop bit of the character in process is shifted out. Transmission is resumed after the
CTS input returns to a logic 0, indicating more data may be sent.
With the Auto-RTS function enabled, an interrupt is generated when the receive FIFO
reaches the programmed trigger level. The RTS pin will not be forced to a logic 1
(RTS off), until the receive FIFO reaches the next trigger level. However, the RTS pin
will return to a logic 0 after the data buffer (FIFO) is unloaded to the next trigger level
below the programmed trigger level. However, under the above described conditions,
the SC16C750 will continue to accept data until the receive FIFO is full.
6.4 Time-out interrupts
When two interrupt conditions have the same priority, it is important to service these
interrupts correctly. Receive Data Ready and Receive Time Out have the same
interrupt priority (when enabled by IER[0]). The receiver issues an interrupt after the
number of characters have reached the programmed trigger level. In this case, the
SC16C750 FIFO may hold more characters than the programmed trigger level.
Following the removal of a data byte, the user should re-check LSR[0] for additional
characters. A Receive Time Out will not occur if the receive FIFO is empty. The
time-out counter is reset at the center of each stop bit received or each time the
receive holding register (RHR) is read. The actual time-out value is 4 character time.
64-byte FIFO
1
16
1
16
32
8
32
56
16
56
60
32
Table 4:
Flow control mechanism…continued
Selected trigger level
(characters)
INT pin activation
Negate RTS
Assert RTS