Asynchronous Serial Port
10-11
10.2.3
Serial Port 0/1 Transmit Registers
(SP0TD/SP1TD, Offset 84h/14h)
The transmit registers (Figure 10-5) are written by software with the value to be transmitted
over the serial interface. The transmitter is double-buffered; data to be transmitted is copied
from the transmit register to the transmit shift register (which is not accessible to software)
before transmitting. The state of the transmit and transmit shift registers is reflected in the
TEMT and THRE bits in the associated Serial Port Status register.
When hardware handshaking is enabled, the transmitter will not transmit data while RTS/
RTR inputs are deasserted. Data is held in the transmit and transmit shift registers without
affecting the transmit pin.
The serial port transmit register in the Am186EM and Am188EM microcontrollers is
renamed in the Am186ES and Am188ES microcontrollers as the Serial Port 0 Transmit
register.
Figure 10-5
Serial Port 0/1 Transmit Registers
The value of SPTD at reset is undefined.
Bits 15–8: Reserved
Bit 7–0: Transmit Data (TDATA)—This field contains data to be transmitted through the
asynchronous serial port.
15
7
0
Reserved
TDATA
Summary of Contents for Am186 ES
Page 1: ...Am186 ES and Am188 ES User s Manual...
Page 4: ...iv...
Page 12: ...Table of Contents xii...
Page 22: ...Features and Performance 1 8...
Page 60: ...System Overview 3 28...
Page 84: ...Chip Select Unit 5 14...
Page 132: ...Timer Control Unit 8 8...
Page 166: ...Programmable I O Pins 11 6...
Page 184: ...Register Summary A 18...