sc16c652 NXP Semiconductors, sc16c652 Datasheet - Page 9

• Manufacturer Part Number: sc16c652
• Description: Dual Uart With 32 Bytes Of Transmit And Receive Fifos
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 11634
Product data
6.4 Hardware flow control
6.5 Software flow control
Table 5:
When automatic hardware flow control is enabled, the SC16C652 monitors the CTS
pin for a remote buffer overflow indication and controls the RTS pin for local buffer
overflows. Automatic hardware flow 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
flow control request, ISR[5] will be set to a logic 1 (if enabled via IER[6,7]), and the
SC16C652 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 SC16C652 will continue to accept data until the receive FIFO is full.
When software flow control is enabled, the SC16C652 compares one or two
sequential receive data characters with the programmed Xon or Xoff character
value(s). If received character(s) match the programmed Xoff values, the SC16C652
will halt transmission (TX) as soon as the current character(s) has completed
transmission. When a match occurs, the receive ready (if enabled via Xoff IER[5])
flags will be set and the interrupt output pin (if receive interrupt is enabled) will be
activated. Following a suspension due to a match of the Xoff characters’ values, the
SC16C652 will monitor the receive data stream for a match to the Xon1,2 character
value(s). If a match is found, the SC16C652 will resume operation and clear the flags
(ISR[4]).
Reset initially sets the contents of the Xon/Xoff 8-bit flow control registers to a logic 0.
Following reset, the user can write any Xon/Xoff value desired for software flow
control. Different conditions can be set to detect Xon/Xoff characters and
suspend/resume transmissions. When double 8-bit Xon/Xoff characters are selected,
the SC16C652 compares two consecutive receive characters with two software flow
control 8-bit values (Xon1, Xon2, Xoff1, Xoff2) and controls TX transmissions
accordingly. Under the above described flow control mechanisms, flow control
characters are not placed (stacked) in the user accessible RX data buffer or FIFO.
When using a software flow control the Xon/Xoff characters cannot be used for data
transfer.
Selected trigger level
(characters)
8
16
24
28
Flow control mechanism
Rev. 04 — 20 June 2003
Dual UART with 32 bytes of transmit and receive FIFOs
INT pin activation
8
16
24
28
Negate RTS or
send Xoff
16
24
28
28
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
SC16C652
Assert RTS or
send Xon
0
7
15
23
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