Asynchronous Serial Ports (UARTs)
Am186™CC/CH/CU Microcontrollers User’s Manual
13-9
The OER bit in the (H)SPSTAT status register is set to 1 when the receiver has a data
overrun error. When extended reads are enabled, the OER bit in the (H)SPRXD receive
data register is set to 1, and then a 1 is written to the OER bit in the status register.
When FIFOs are enabled, the OER bit in the receive data register is passed through the
FIFO with the last character of overrun data (i.e., the first data character after the overrun
loss). The OERIM bit was added to provide an immediate interrupt. This bit bypasses the
FIFO; OERIM is set immediately after the overflow occurs.
Both the OER and OERIM bits must be cleared by software.
13.5.2.2
Address Bits
When set, an
address bit indicates that the present frame is a special frame. On the
microcontroller, address bit generation and detection are supported in 7- or 8-data-bit
frames. When the address bit is set, the other 7 or 8 bits of data in the frame are interpreted
as a code; which type of code depends on the configuration. All transmissions that follow
this address frame are directed as specified until another frame is received with the address
bit enabled and with a different code.
One possible use for the code following the address bit (resulting in its name) is for the
address of a slave peripheral device on a
multidrop (also called multipoint) serial line, where
one master device is talking to multiple slave devices. Although named an address bit, this
bit actually behaves as an extended bit that may set an interrupt; the data bits that follow
the bit do not need to be used as an address. Another possible use is for encoded discrete
commands (e.g., sending a hang-up command to a modem). What the code is used for,
and how, is determined by software.
To use the address bit in the microcontroller, the ABEN and D7 bits in the (H)SPCON0
register must be configured. In addition, the transmit AB bit must be set for a transmit; the
received AB bit is set by hardware for a receive.
When the ABEN bit is set to 1, address bits are enabled. If the D7 bit is 0, serial frames
contain a low start bit, eight data bits, an optional address bit, then one or two High stop
bits (transmitted least significant bit first). If the D7 bit is set to 1, serial frames contain a
low start bit, seven data bits, an optional address bit, and one or two stop bits.
13.5.2.2.1
Transmitting with Address Bit Set
When ABEN is set in a transmit, the transmit AB field of the (H)SPCON0 register is sent
as the MSB bit after the 7 or 8 data bits in TDATA.
When extended writes are enabled (EXDWR = 1), the transmit AB bit in the (H)SPTXD
register is used instead. Because this register also contains the data to be transmitted, this
allows a single write to replace the two writes needed when extended writes are not enabled.
When extended writes are enabled, the (H)SPTXD register supports word-wide DMA
transfers.
When extended writes are not enabled, the value of the transmit AB field is sampled during
the transmission of the final data bit and is used to determine the value of the TXD signal
for one bit time following the last data bit and before the transmission of the stop bit. The
transmit AB field is cleared by the UARTs after reading its value. Because the transmit AB
bit is not double buffered, software that intends to send a frame with the address bit set
must wait until the transmitter is empty (TEMT=1) before setting the transmit AB bit and
writing the data for the next frame into the transmit data register.
Содержание Am186 CC
Страница 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Страница 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Страница 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Страница 39: ...Architectural Overview Am186 CC CH CU Microcontrollers User s Manual 1 15 Figure 1 6 32 Channel Linecard CH CC...
Страница 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Страница 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Страница 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Страница 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Страница 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...