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Frequently asked questions

16C UART Feature FAQ

Q Can 16C UARTs be used for wireless transmission?
A Yes, 16C UARTs contain an IrDA decoder/encoder which can be used to transmit data via wireless infrared signals.
Q Our embedded design uses an MC68000 controller from Motorola. We would like to add a UART to the design. Can your UARTs be easily connected to such a processor?
A Two of our quad-channel 16C UART devices (the SC16C554B and the SC16C654B) provide a seamless interface to this processor. These UARTs have a configuration pin which selects the bus interface for these UARTs to be an Intel or a Motorola interface.
Q Do any of your single-channel 16C UART devices have auto hardware flow control like the TI 16C550 has?
A Yes, our SC16C550B does.
Q We are using a TI 16C550, and this device has auto hardware flow control (MCR bit 5). Does your SC16C550B have this feature?
A Our SC16C550B does support auto hardware flow control and software flow control through MCR register bit 5.
Q The Exar 16C650 always does a single-byte DMA transfer. Does your SC16C650B do the same?
A Yes, it does.
Q What is the auto hardware flow control in the 16C654, and how do I use it?
A Auto hardware flow control is the ability of the UART receiver to tell the remote UART to stop sending without intervention from a micro controller. It does this by negating the /RTS signal once the receive FIFO has reached a programmed trigger level. You can use this feature by programming the trigger level in FCR register, and then turning on the RTS and CTS bits in the EFR register. Other UARTs which include an automatic hardware flow control are the SC16C550B, SC16C650B, SC16C652B, SC16C2550, SC16C554, SC16C750B, and SC16C752B.
Q What does auto software flow control mean?
A
Auto software flow control is similar to hardware flow control, that is, the ability of a UART to tell the remote UART to stop or start sending more data. The difference is that, instead of using a signal on an RTS or CTS hardware pin, the UART sends a specific character in the data stream. This byte is called the XOFF or XON character.
If the programmed receive trigger level is reached, the UART sends XOFF to the remote UART to tell it to stop sending. Once the host empties the receive FIFO (or the next lower trigger level is reached), the UART automatically sends XON to tell the remote UART to start sending again.
Q Presently, we have a multi-channel board that uses four 16C550 40-pin DIP package UARTs. We are thinking about redesigning this board to use a single device that has four built-in 16C550-compatible UARTs. Which NXP Semiconductors device should I use for this redesign?
A Our SC16C654B or SC16C554B can be used for your design. If you do not need the advanced features of the 16C654B, such as the deeper FIFOs (64-byte vs. 32-byte), then you could use the 16C554B. Both these devices have four built-in 16C550-compatible UARTs. They are backwards software compatible to the industry-standard 16C550 devices.
Q
Does you make a UART with the following requirements?
  • Single channel
  • Baud rate from 9.6K to 115.2K
  • Start bit = 1, data = 8, parity even, stop = 1
  • FIFO of four bytes or more
  • Small footprint
  • Available for the next 5 to 15 years
A Our SC16C550B device meets all of you requirements. This is a single-channel device. It can operate up to 1.5Mbps, has a 16-byte FIFO, and is available in a 44-pin PLCC or 48-pin LQFP package. This device can also operate in 2.5V, 3.3V, or 5V environments.
Q How does DMA in the UART work?
A Performing DMA with the UART refers to using interrupt block mode. That is, the processor can send and receive the data to and from the UART in a block. This method has lower overhead.
Q Is a UART 8-bit or 16-bit?
A UART have an 8-bit data bus.
Q How long does it take the UART to wake up from standby?
A It takes a few millisecond for the UART to wakeup from sleep and stabilize.
Q Can the 16C UART perform the IrDA protocol basics in it, or does it merely handle the encoding/decoding?
A UARTs have the encoding/decoding circuits built in, but not the IrDA protocols.

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