Overview
| Information | 1.62V to 3.63V UART with 64-Byte FIFO and VLIO Interface |
|---|---|
| Data Bus Interface | VLIO |
| # of Channels | 1 |
| Max Data Rate 5V (Mbps) | na |
| Max Data Rate 3.3V (Mbps) | 20 |
| Max Data Rate 2.5V (Mbps) | 16 |
| Max Data Rate 1.8V (Mbps) | 10 |
| Tx FIFO (Bytes) | 64 |
| Rx FIFO (Bytes) | 64 |
| Auto Flow Control | ✔ |
| Auto RS-485 Half-Duplex Control | ✔ |
| Multidrop (9-bit) Mode | ✔ |
| Fractional Baud Rate Generator | ✔ |
| Power Down Mode | ✔ |
| Supply Voltage Range VCC (V) | 1.62 to 3.63 |
| Auto RTS/CTS | ✔ |
| Package | QFN-32 |
| FIFO Level Counters | ✔ |
| Selectable/ Programable Trigger Levels | P |
| IrDA Sup | ✔ |
| 5V Tolerant Inputs | |
| Max UART/GPIO Input Voltage (V) | VCC |
| Max UART/GPIO Output Voltage (V) | VCC |
| Temperature Range (°C) | -40 to 85 |
The XR16M781¹ (M781) is an enhanced Universal Asynchronous Receiver and Transmitter (UART) with a VLIO bus interface and has 64 bytes of transmit and receive FIFOs, programmable transmit and receive FIFO trigger levels, automatic hardware and software flow control, and data rates of up to 20 Mbps at 3.3V, 16 Mbps at 2.5V and 10 Mbps at 1.8V with 4X data sampling rate.
The Auto RS-485 Half-Duplex Direction control feature simplifies both the hardware and software for half-duplex RS-485 applications. In addition, the Multidrop mode with Auto Address detection increases the performance by simplifying the software routines.
The Independent TX/RX Baud Rate Generator feature allows the transmitter and receiver to operate at different baud rates. Power consumption of the M781 can be minmized by enabling the sleep mode and PowerSave mode.
The M781 has a 16550 compatible register set that provide users with operating status and control, receiver error indications, and modem serial interface controls. An internal loopback capability allows onboard diagnostics. The M781 is available in 24-pin QFN, 32-pin QFN and 25-pin BGA packages.
NOTE: ¹ Covered by U.S. Patent #5,649,122.
- VLIO bus interface
- Pin-to-pin compatible with SC16C850V and SC16C850SV in 32-QFN package
- 20 Mbps maximum data rate
- Programmable TX/RX FIFO Trigger Levels
- TX/RX FIFO Level Counters
- Independent TX/RX Baud Rate Generator
- Fractional Baud Rate Generator
- Auto RTS/CTS Hardware Flow Control
- Auto XON/XOFF Software Flow Control
- Auto RS-485 Half-Duplex Direction Control
- Multidrop mode w/ Auto Address Detect
- Sleep Mode with Automatic Wake-up
- PowerSave mode
- Infrared (IrDA 1.0 and 1.1) mode
- 1.62V to 3.63V supply operation
- Crystal oscillator or external clock input
- Personal Digital Assistants (PDA)
- Cellular Phones/Data Devices
- Battery-Operated Devices
- Global Positioning System (GPS)
- Bluetooth
Documentation & Design Tools
All Types
Data Sheets
Application Notes
Schematics & Design Files
Product Briefs & Brochures
Design Tools & Simulation
User Guides & Manuals
| Type | Title | Version | Date | File Size |
|---|---|---|---|---|
| Data Sheets | XR16M781 1.62V to 3.63V UART with 64-Byte FIFO and VLIO Interface | 1.0.1 | August 2009 | 1.1 MB |
| Application Notes | DAN-190, MaxLinear UARTs in RS-485 Applications | R01 | July 2023 | 2.4 MB |
| Application Notes | AN-204, UART Sleep Mode | 1.0.0 | June 2010 | 515.8 KB |
| Application Notes | DAN-200, MULTIDROP/9-BIT MODE Feature | 1 | April 2009 | 143.5 KB |
| Application Notes | DAN-201, Independant TX and RX Baud Rate Generator | 1 | April 2009 | 144.2 KB |
| User Guides & Manuals | XR16M781 User Manuals | 1.0.0 | June 2009 | 416.8 KB |
| Product Flyers | 1.62V to 3.63V High Performance UARTs | 1.0.0 | March 2009 | 361.9 KB |
| Product Brochures | Interface Brochure | R02 | November 2024 | 3.6 MB |
| Schematics & Design Files | Schematics | 1.0.0 | June 2009 | 57.1 KB |
Simulation Models
| Package Type | Vcc | Temp | Mode | Version | File |
|---|---|---|---|---|---|
| BGA | 1.8V | Industrial | Intel | 1 | |
| BGA | 2.5V | Industrial | Intel | 1 | |
| BGA | 3.3V | Industrial | Intel | 1 | |
| QFN | 1.8V | Industrial | Intel | 1 | |
| QFN | 2.5V | Industrial | Intel | 1 | |
| QFN | 3.3V | Industrial | Intel | 1 | |
| QFN | 1.8V | Industrial | Intel | 1 | |
| QFN | 2.5V | Industrial | Intel | 1 | |
| QFN | 3.3V | Industrial | Intel | 1 |
Quality & RoHS
| Part Number | RoHS | Exempt | RoHS | Halogen Free | REACH | TSCA | MSL Rating / Peak Reflow | Package |
|---|---|---|---|---|---|---|---|
| XR16M781IL32-F | N | Y | Y | Y | Y | L2 / 260ᵒC | QFN32 5x5 OPT3 |
Click on the links above to download the Certificate of Non-Use of Hazardous Substances.
Additional Quality Documentation may be available, please Contact Support.
Parts & Purchasing
| Part Number | Pkg Code | Min Temp | Max Temp | Status | Suggested Replacement | PDN |
|---|---|---|---|---|---|---|
| XR16M781IB25-F | BGA25 | -40 | 85 | OBS | XR16M781IL24-F , XR16M781IL32-F | |
| XR16M781IB25TR-F | BGA25 | -40 | 85 | OBS | XR16M781IL24TR-F , XR16M781IL32TR-F | |
| XR16M781IL24-F | QFN24 4x4 OPT1 | -40 | 85 | OBS | ||
| XR16M781IL24TR-F | QFN24 4x4 OPT1 | -40 | 85 | OBS | ||
| XR16M781IL32-F | QFN32 5x5 OPT3 | -40 | 85 | OBS | ||
| XR16M781IL32TR-F | QFN32 5x5 OPT3 | -40 | 85 | OBS | XR16M781IL32-F |
Part Status Legend
Active - the part is released for sale, standard product.
EOL (End of Life) - the part is no longer being manufactured, there may or may not be inventory still in stock.
CF (Contact Factory) - the part is still active but customers should check with the factory for availability. Longer lead-times may apply.
PRE (Pre-introduction) - the part has not been introduced or the part number is an early version available for sample only.
OBS (Obsolete) - the part is no longer being manufactured and may not be ordered.
NRND (Not Recommended for New Designs) - the part is not recommended for new designs.
Active - the part is released for sale, standard product.
EOL (End of Life) - the part is no longer being manufactured, there may or may not be inventory still in stock.
CF (Contact Factory) - the part is still active but customers should check with the factory for availability. Longer lead-times may apply.
PRE (Pre-introduction) - the part has not been introduced or the part number is an early version available for sample only.
OBS (Obsolete) - the part is no longer being manufactured and may not be ordered.
NRND (Not Recommended for New Designs) - the part is not recommended for new designs.
Packaging
| Pkg Code | Details | Quantities | Dimensions |
|---|---|---|---|
| QFN24 4x4 OPT1 |
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| QFN32 5x5 OPT3 |
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Notifications
FAQs & Support
Search our list of FAQs for answers to common technical questions.
For material content, environmental, quality and reliability questions review the Quality tab or visit our Quality page.
For ordering information and general customer service visit our Contact Us page.
Submit a Technical Support Question As a New Question
LSR bit-6 is a superset of LSR bit-5. The transmitter consists of a TX FIFO (or THR only when FIFOs are not enabled) and a Transmit Shift Register (TSR). When LSR bit-5 is set, it indicates that the TX FIFO (or THR) is empty, however there may be data in the TSR. When LSR bit-6 is set, it indicates that the transmitter (TX FIFO + TSR) is completely empty.
You can tell by reading LSR bit-5 or bit-6. If they are '0', then the transmit interrupt was generated by the trigger level. If they are '1', then the transmit interrupt was generated by the TX FIFO becoming empty. For enhanced UARTs, you can just read the FIFO level counters.
An RX Data Ready interrupt is generated when the number of bytes in the RX FIFO has reached the RX trigger level. An RX Data Timeout interrupt is generated when the RX input has been idle for 4 character + 12 bits time.
For some UARTs, the RX Data Timeout interrupt has a higher priority and in others, the RX Data Ready interrupt has a higher priority. See the interrupt priority section of the datasheet.
The UART requires a clock and a valid baud rate in order to transmit and receive data. Check that there is a clock signal on the XTAL1 input pin. Also, valid divisors need to be written into the DLL and DLM registers. Most UARTs have random (invalid) values upon power-up.
For most UARTs, the interrupt is generated when the data is ready to be read from the RX FIFO. The are some UARTs that generate the interrupt when the character with the error is received. There are some UARTs that have a register bit to select whether the LSR interrupt is generated immediately or delayed until it is ready to be read.
The UART will enter the sleep mode if the following conditions have been satisfied for all channels:
-Sleep Mode is enabled
-No interrupts are pending
-TX and RX FIFOs are empty
-RX input pin is idling HIGH (LOW in IR mode)
-Valid values in DLL and DLM registers
-Modem input pins are idle (MSR bits 3-0=0x0)
See AN204, UART Sleep Mode for more information on UART Sleep Mode
The UART will wake-up from sleep mode by any of the following conditions on any channel:
-Sleep mode is disabled
-Interrupt is generated
-Data is written into THR
-There is activity on the RX input pin
-There is activity on the modem input pins
If the sleep mode is still enabled and all wake-up conditions have been cleared, it will return to the sleep mode.
See AN204, UART Sleep Mode for more information on UART Sleep Mode
There will be no activity on the XTAL2 output.
See AN204, UART Sleep Mode for more information on UART Sleep Mode
For any UART that has the wake-up indicator interrupt, an interrupt will be generated when the UART wakes up even if no other interrupts are enabled.
See AN204, UART Sleep Mode for more information on UART Sleep Mode
No, Auto RTS and Auto CTS are independent. Auto RTS is toggled by the UART receiver. Auto CTS is monitored by the UART Transmitter.
No, Auto RTS and Auto CTS will work normally without the interrupts enabled.
No, software flow control characters are not loaded into the RX FIFO.
Since 2-character software flow control requires that 2 consecutive flow control characters match before data transmission is stopped or resumes, there is less of a chance that data transmission is stopped because one data byte matched a control character.
Auto RS485 Half-Duplex Control feature overrides the Auto RTS flow control feature if both features use the RTS# output pin. Both features can only be used simultaneously if the Auto RS485 control output is not the RTS# output. For some UARTs, the Auto RS485 control output is not the RTS# output.
Most UARTs use RTS#, however the XR16C850 and XR16C864 use the OP1# output as the Auto RS485 control output. In addition to using the RTS# output as the Auto RS485 control output, the XR16L784, XR16L788 and XR16V798 can use the DTR# output as the Auto RS485 control output.
The polarity of the RS485 control output varies from one UART to another. For some UARTs, an inverter may be required. Some of the newer UARTs have register bits that can change that polarity of the RS485 control output.
In the normal mode, the TX interrupt is generated when the TX FIFO is empty, and there may still be data in the Transmit Shift Register. In the RS485 mode, the TX interrupt is generated when the TX FIFO and the TSR register are both empty.
It is recommended that the FIFO counters at the Scratchpad Register location be used. When transmitting or receiving data, writing to the LCR register could result in transmit and/or receive data errors.
Due to the dynamic nature of the FIFO counters, it is recommended that the FIFO counter registers be read until consecutive reads return the same value.
All of the UARTs that have the IR mode supports up to 115.2Kbps as specified in IrDA 1.0. The newer I2C/SPI UARTs can support up to 1.152Mbps as specified in IrDA 1.1.
For external clock frequencies above 24MHz at the XTAL1 input, a 2K pull-up may be necessary to improve the rise times if there are data transmission errors.
Yes, you can daisy-chain it like that, but only up to 2 times (3 UARTs total in the daisy-chain). The UARTs should be as close as possible.
No, it just has to meet the minimum high and low pulse widths.
Yes, if you are using a UART with a fractional baud rate generator. This provides a divisor feature with a granularity of 1/16, allowing for any baud rate to be generated by any clock frequency, standard or non-standard. Click on the parametric search button of the product family page and find the Fractional Baud Rate Generator column which tells which products have this feature.
They crystal oscillator circuitry is recommended for fundamental frequency crystals only. The maximum frequency for crystals with fundamental frequencies is typically 24MHz. Above that frequency, crystals operate at higher harmonics, which will not work with the recommended crystal oscillator circuitry.
No. It is only required for transmitting and receiving data.
The -F suffix indicates ROHS / Green compliance:
https://www.exar.com/quality-assurance-and-reliability/lead-free-program
https://www.exar.com/quality-assurance-and-reliability/lead-free-program
Visit the product page for the part you are interested in. The part's status is listed in the Parts & Purchasing section. You can also view Product Lifecycle and Obsolescence Information including PDNs (Product Discontinuation Notifications).
To visit a product page, type the part into the search window on the top of the MaxLinear website.
In this example, we searched for XRA1201. Visit the product page by clicking the part number or visit the orderable parts list by clicking "Orderable Parts".
The Parts & Purchasing section of the product page shows the Status of all orderable part numbers for that product. Click Show obsolete parts, to see all EOL or OBS products.
It depends on the baud rate. For example, for a start bit, 8 data bits, no stop bit and 1 stop bit, the maximum baud rate deviation is 4.76%. For more information, see https://www.exar.com/appnote/dan108.pdf
Please check that all the following conditions are satisfied first.
- no interrupts pending (ISR bit-0 = 1)
- modem inputs are not toggling (MSR bits 0-3 = 0)
- RX input pin is idling HIGH • divisor (the value in DLL register) is non-zero
- TX and RX FIFOs are empty
Be sure sleep mode bit has been set to 1. If there are multiple UART channels, the sleep conditions must be true for all channels.
See more on Sleep Mode in AN204 UART Sleep Mode.
Yes. Note: some devices do have powersave mode. If UART goes into powersave mode, then the registers are not accessible.
See more on Sleep Mode in AN204 UART Sleep Mode.
Read LSR register to check whether the UART receives the data or not.
- If LSR value is 0x60, it means that either UART receiver FIFO doesn’t receive the data or the data in receiver FIFO has been read out before the read of LSR.
- If LSR value is 0x00, it means data is still in the THR (clock doesn’t oscillate to transmit data).
- If LSR value is 0xFF, it means either UART is in powersave mode or UART is powered off. For those devices with powersave mode, be sure that UARTS are not in powersave mode.
See more on Sleep Mode in AN204 UART Sleep Mode.
- Check whether the register set can be accessed.
- Check whether the crystal is oscillating fully.
- Check whether the data can be transmitted in internal loopback mode.
See more on Sleep Mode in AN204 UART Sleep Mode.
Videos
MxL UARTs Auto RS-485 Direction Control
This video describes how the automatic RS-485 half-duplex direction control feature in MaxLinear UARTs reduces driver development and frees up CPU/MCU loading. This feature eliminates the need to monitor the status of the UART’s transmit shift register and automatically switches MaxLinear RS-485 transceivers from the transmit mode to the receive mode. This video summarizes the content in application note DAN-190.
