sc16c654 NXP Semiconductors, sc16c654 Datasheet - Page 14

• Manufacturer Part Number: sc16c654
• Description: Quad Uart With 64-byte Fifo And Infrared Irda Encoder/decoder
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 11617
Product data
6.6 Hardware flow control
6.7 Software flow control
interrupt is generated whenever the Receive Holding Register (RHR) has not been
read following the loading of a character or the receive trigger level has not been
reached. (For a description of this timing, see
Table 6:
When automatic hardware flow control is enabled, the SC16C654/654D 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
SC16C654/654D 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. However, under the above described conditions, the
SC16C654/654D will continue to accept data until the receive FIFO is full.
When software flow control is enabled, the SC16C654/654D compares one or two
sequential receive data characters with the programmed Xon/Xoff or Xoff1,2
character value(s). If received character(s) match the programmed values, the
SC16C654/654D 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 SC16C654/654D will monitor the receive data stream for a match to the Xon1,2
character value(s). If a match is found, the SC16C654/654D will resume operation
and clear the flags (ISR[4]). The SC16C654/654D offers a special Xon mode via
MCR[5]. The initialized default setting of MCR[5] is a logic 0. In this state, Xoff and
Xon will operate as defined above. Setting MCR[5] to a logic 1 sets a special
operational mode for the Xon function. In this case, Xoff operates normally, however,
transmission (Xon) will resume with the next character received, i.e., a match is
declared simply by the receipt of an incoming (RX) character.
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
Selected trigger level
(characters)
8
16
56
60
RX trigger levels
Quad UART with 64-byte FIFO and infrared (IrDA) encoder/decoder
Rev. 04 — 19 June 2003
INT pin activation
8
16
56
60
Section 6.6 “Hardware flow
Negate RTS or
send Xoff
(characters)
16
56
60
60
SC16C654/654D
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
Assert RTS or
send Xon
(characters)
0
7
15
55
control”.)
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