Z80189 Datasheet, PDF (86/107 Pages) Zilog, Inc. – GENERAL-PURPOSE EMBEDDED CONTROLLERS

Zilog
PRELIMINARY
PC DMA MAILBOX DATA REGISTERS
Z80189/Z8L189
GENERAL-PURPOSE EMBEDDED CONTROLLERS
765 43210
10010001
765 43210
00000000
Figure 103. Host DMA Transmit Register, HDMAT0
(Z180 MPU Read Only Address XXD0H)
(PC Write Only)
Note: 91hex is defaulted into this register to indicate
revision (9 for Z189 and 1 for 1st revision). Once the
revision data is read by the Z180 CPU, bit 6 of the HMC
register (Revision Data Avail bit) will be read as zero.
765 43210
00000000
Figure 104. Host DMA Receive Register, HDMAR0
(Z180 MPU Write Only Address XXD0H)
(PC Read Only)
Figure 105. Host DMA Transmit Register, HDMAT1
(Z180 MPU Read Only Address XXD1H)
(PC Write Only)
HDMAT1 can also be used as a HOST OUTPUT MAILBOX
DATA REGISTER. Refer to Host Output Mailbox function
for details.
765 43210
00000000
Figure 106. Host DMA Receive Register, HDMAR1
(Z180 MPU Write Only Address XXD1H)
(PC Read Only)
HOST INPUT/OUTPUT MAILBOX ENHANCEMENTS
The purpose of Host I/O Mailbox is to provide an additional
data path between PC HOST and Z80189 in a Modem
Control Application. This is required in order to accommo-
date transfer of data other than data (flows through COM
Port) or audio (flows through PC DMA MAILBOX). An
example implementation of this feature is described
below:
– PC HOST controlled COM Port selection. In a Psuedo
"Plug & Play" environment, the PC BIOS will assign a
modem to a COM Port address upon powerup. There-
fore, the Modem will need to "listen" to the PC bus for
BIOS calls that query the existence of a modem card.
The modem will then need to reply and output informa-
tion on its capabilities and requirements. The PC BIOS
will then assign the Modem to a COM Port and interrupt
such that there are no resource conflicts.
In order to facilitate the feature listed above, a communica-
tion path needs to be available between a PC BIOS and
Modem PRIOR to the selection of COM Port, DMA, or IRQ
selection.
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DS971890301