Zilog Z08470 - Manual (Page 278)

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UM008101-0601 Serial Input/Output
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information field may be sent to the Z80 SIO using the Transmit Interrupt
mode. The Z80 SIO transmits the Frame Check sequence using the
Transmit Underrun feature.
When the transmitter is first enabled, it is already empty and cannot then
become empty. Therefore, no Transmit Buffer Empty interrupts can occur
until after the first data character is written.
Data Transfer Using WAIT/READY
When the Wait/Ready function is selected, WAIT communicates to the
CPU that the Z80 SIO is not ready to accept the data and that the CPU must
extend the I/O cycle. To a DMA controller, READY communicates that the
transmitter buffer is empty and that the Z80 SIO is ready to accept the next
character. If the data character is not loaded to the Z80 SIO by the time the
transmit shift register is empty, the Z80 SIO enters the Transmit Underrun
condition. Address, control, and information fields may be transferred to
Table 8. Contents of Write Registers 3, 4, and 5 in SDLC Modes
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
WR
3 00 = Rx 5 Bits Char
10 = Rx 6 Bits Char
01 = Rx 7 Bits Char
11 = Rx 8 Bits Char Auto
Enables Enter Hunt
Mode (if
incoming
data not
needed) Rx CRC
Enable Address
Search
Mode 0 Rx
Enable
WR
4 0 0 1
Selects
SDLC
Mode 0
Selects
SDLC
Mode 0 0 0 0
WR
5 DTR 00 = Tx 5 Bits (or less)
Char
10 = Tx 6 Bits Char
01 = Tx 7 Bits Char
11 = Tx 8 Bits Char 0 Tx Enable 0
Selects
SDLC
CRC
RTS Tx CRC
Enable