Z80189 Datasheet, PDF (64/107 Pages) Zilog, Inc. – GENERAL-PURPOSE EMBEDDED CONTROLLERS

Zilog
16550 MIMIC INTERFACE
PRELIMINARY
Z80189/Z8L189
GENERAL-PURPOSE EMBEDDED CONTROLLERS
The Z80189 has a 16550 MIMIC interface that allows it to
mimic the 16550 device. It has all the interface pins
necessary to connect up to the PC/XT/AT bus without any
extra circuitry. It contains the complete register set of the
16550 part with the same interrupt structure. The data path
allows parallel transfer of data to and from the register set
by the internal Z80180 of the Z80189. There is no shift
register associated with the MIMIC of the 16550 UART.
This interface saves the application from doing a serial
transfer before performing data compression or error
correction on the data.
An additional two 8-bit timers are available for program-
ming the FIFO time-out feature (4 Character Time Emula-
tion) for both Receiver and Transmitter FIFO’s.
The 16550 MIMIC interface supports the PC/XT/AT inter-
rupt structure as well as an additional mode that allows for
a wired AND interrupt structure.
All registers of the 16550 MIMIC interface are accessible
in any page of I/O space since only the lowest 8 address
lines are decoded.
Control of the register set is maintained by six priority
encoded interrupts to the Z80189. When the PC/XT/AT
writes to THR, MCR, LCR, DLL, DLM, FCR or reads the
RBR, an interrupt to the Z80189 is generated. Each inter-
rupt can be individually masked off or all interrupts can be
disabled by writing a single bit. Both mode 0, mode 1 and
mode 2 interrupts are supported by the 16550 MIMIC
interface.
Two 8-bit timers are also available to control the data
transfer rate of the 16550 MIMIC interface. Their input is
tied to the BRG clock so a down count of 24 bits is possible.
COM Port Decode functionality is integrated into the Z189.
This allows the MIMIC to be selected for a specific COM
Port Address (PC COM Port Address 1-4). Previously for
the Z80182, the COM Port Address selected for the MIMIC
was implemented through external COM Port Decode
circuitry. The COM Port Decode circuitry in the Z80189
simplifies this process by allowing the user to select the
MIMIC Com Port addresses through software, as well as
reducing the system board level costs by saving board
space and external circuitry.
See Figure 76 for a block diagram of the 16550 MIMIC
interface.
PC Side
10
Selectable
COM Port Decode
180 Side
Host Addr Decode ₄
Host Data Bus
8
PC IRQ
1
PC DMA Control
4
16550 MIMIC
Register Set
6
D
A
T
A
PC Host IRQ
B
U
S
PC DMA Mailbox
and I/O Mailbox
Rx Timer
Tx Timer
Z80180
IRQ &
Control
Control
Config
Register
Z80180
Address
8
Z80180 Data Bus
Figure 76. 16550 MIMIC Block Description
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