Z80181 Zilog., Z80181 Datasheet - Page 33

• Manufacturer Part Number: Z80181
• Description: SMART ACCESS CONTROLLER (SAC)
• Manufacturer: Zilog.

Zilog
Time Constant Word
Before a channel can start counting, it must receive a time
constant word. The time constant value may be anywhere
between 1 and 256, with “0” being accepted as a count of
256 (Figure 47).
SCC REGISTERS
For more detailed information, please refer to the Z8030/
Z8530 SCC Technical Manual.
Note:
The Address for the Control/Status Register is E8h. The
Address for the Data Register is E9h.
Bit
RR0
RR1
RR2
RR3
RR6
DS971800500
Description
Transmit and Receive buffer status
(only when enabled).
and external status.
Special Receive Condition status.
Interrupt vector (modified if VIS Bit in WR9 is set).
Interrupt pending bits.
SDLC FIFO byte counter lower byte
Figure 47. CTC Time Constant Word
D7 D6 D5 D4 D3 D2 D1 D0
Table 2. SCC Read Registers
TC0
TC1
TC2
TC3
TC4
TC5
TC6
TC7
Interrupt Vector Word
If one or more of the CTC channels have interrupt enabled,
then the Interrupt Vector Word is programmed. Only the
five most significant bits of this word are programmed, and
bit D0 must be “0”. Bits D2-D1 are automatically modified
by the CTC channels after responding with an interrupt
vector (Figure 48).
Read Registers
The SCC contains eight read registers. To read the con-
tents of a register (rather than RR0), the program must first
initialize a pointer to WR0 in exactly the same manner as a
write operation. The next I/O read cycle will place the
contents of the selected read registers onto the data bus
(Figure 49).
Bit
RR7
RR8
RR10
RR12
RR13
RR15
D7 D6 D5 D4 D3 D2 D1 D0
Description
SDLC FIFO byte count and status
Figure 48. CTC Interrupt Vector Word
(only when enabled).
Receive buffer.
Miscellaneous status bits.
Lower byte of baud rate.
Upper byte of baud rate generator time constant.
External Status interrupt information.
Addr: E4h
S
MART
A
0 Interrupt Vector Word
1 Control Word
Channel Identifier
(Automatically Inserted
by CTC)
Supplied By User
CCESS
0 0 Channel 0
0 1 Channel 1
1 0 Channel 2
1 1 Channel 3
C
ONTROLLER
Z80181
2-33
SAC
™