Z80 Datasheet, PDF (258/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

< %27 2GTKRJGTCNU
7UGT /CPWCN
238
character received is loaded into the buffer; the character preceding it is
lost. When the character that has been written over the other characters is
read, the Receive Overrun bit is set and the Special Receive. Condition
vector is returned if Status Affects Vector is enabled.
In a polled environment, the Receive Character Available bit (RR0, D0)
must be monitored so that the Z80 CPU knows when to read a character.
This bit is automatically reset when the receive buffers are read. To prevent
overwriting data in polled operations, the transmit buffer status must be
cheeked before writing to the transmitter. The Transmit Buffer Empty bit is
set to 1 whenever the transmit buffer is empty.
SYNCHRONOUS OPERATION
Overview
Before describing synchronous transmission and reception, the three types
of character synchronization, Monosync, Bisync, and External Sync,
require explanation. These modes use the x1 clock for both Transmit and
Receive operations. Data is sampled on the rising edge of the Receive
Clock input (RxC). Transmitter data transitions occur on the falling edge of
the Transmit Clock input (TxC).
The differences between Monosync, Bisync, and External Sync are in the
form in which initial character synchronization is achieved. The mode of
operation must be selected before sync characters are loaded, because the
registers are used differently in the various modes. Figure 112 depicts the
formats for all three of these synchronous modes.
UM008101-0601
Serial Input/Output