Z80180 Datasheet, PDF (164/326 Pages) Zilog, Inc. – Z8018x Family MPU

Z 8018x Fam ily
M PU Us e r M anual
149
Bit
Position Bit/Field R/W
4
TE
R/W
2–0
SS2–0 R/W
Value Description
Transmit Enable — A CSI/O transmit operation is
started by setting TE to 1. When TE is set to 1, the data
clock is enabled. When in internal clock mode, the data
clock is output from the CKS pin. In external clock mode,
the clock is input on the CKS pin. In either case, data is
shifted out on the TXS pin synchronous with the (internal
or external) data clock. After transmitting 8 bits of data,
the CSI/O automatically clears TE to 0, EF is set to 1, and
an interrupt (if enabled by EIE = 1) is generated. TE and
RE are never both set to 1 at the same time. TE is cleared
to 0 during RESET and IOSTOP mode.
Speed Select — Selects the CSI/O transmit/receive clock
source and speed. SS2, SS I and SS0 are all set to 1 during
RESET. Table 22 shows CSI/O Baud Rate Selection.
CSI/O Transmit/Receive Data Register (TRDR: I/O
Address = 0BH).
TRDR is used for both CSI/O transmission and reception. Thus, the
system design must insure that the constraints of half-duplex operation
are met (Transmit and receive operation cannot occur simultaneously).
For example, if a CSI/O transmission is attempted while the CSI/O is
receiving data, the CSI/O does not work.
TRDR is not buffered. Attempting to perform a CSI/O transmit while the
previous transmit data is still being shifted out causes the shift data to be
immediately updated, thereby corrupting the transmit operation in
progress. Similarly, reading TRDR during a transmit or receive must be
avoided.
UM005001-ZMP0400