Z8 Encore! XP
®
4K Series
Product Specification
95
4. Executes the IRET instruction to return from the interrupt-service routine and await
more data.
Clear To Send (CTS) Operation
The CTS pin, if enabled by the CTSE bit of the UART Control 0 register, performs flow
control on the outgoing transmit datastream. The Clear To Send (CTS) input pin is sam-
pled one system clock before beginning any new character transmission. To delay trans-
mission of the next data character, an external receiver must deassert CTS at least one
system clock cycle before a new data transmission begins. For multiple character trans-
missions, this action is typically performed during Stop Bit transmission. If CTS deasserts
in the middle of a character transmission, the current character is sent completely.
MULTIPROCESSOR (9-bit) Mode
The UART has a MULTIPROCESSOR (9-bit) mode that uses an extra (9th) bit for selec-
tive communication when a number of processors share a common UART bus. In MULTI-
PROCESSOR mode (also referred to as 9-Bit mode), the multiprocessor bit (
MP
) is
transmitted immediately following the 8-bits of data and immediately preceding the Stop
bit(s) as illustrated in
The character format is:
Data Field
lsb
Start
0
1
2
Bit0
Bit1
Bit2
Bit3
Bit4
Bit5
Bit6
msb
Bit7
MP
Stop Bit(s)
1
Idle State
of Line
Figure 13.UART Asynchronous MULTIPROCESSOR Mode Data Format
In MULTIPROCESSOR (9-bit) mode, the Parity bit location (9th bit) becomes the Multi-
processor control bit. The UART Control 1 and Status 1 registers provide MULTIPRO-
CESSOR (9-bit) mode control and status information. If an automatic address matching
scheme is enabled, the UART Address Compare register holds the network address of the
device.
MULTIPROCESSOR (9-bit) Mode Receive Interrupts
When MULTIPROCESSOR mode is enabled, the UART only processes frames addressed
to it. The determination of whether a frame of data is addressed to the UART can be made
in hardware, software or some combination of the two, depending on the multiprocessor
configuration bits. In general, the address compare feature reduces the load on the CPU,
because it does not require access to the UART when it receives data directed to other
PS022815-0206
UART
ZILOG [ ZILOG, INC. ]
