Z80182 Datasheet, PDF (60/109 Pages) Zilog, Inc. – ZILOG INTELLIGENT PERIPHERAL CONTROLLER (ZIP™)

Zilog
PRELIMINARY
Z80182/Z8L182
ZILOG INTELLIGENT PERIPHERAL
/RAMCS AND /ROMCS REGISTERS (Continued)
RAMUBR, RAMLBR RAM Upper Boundary Range,
RAM Lower Boundary Range
These two registers specify the address range for the
/RAMCS signal. When accessed memory addresses are
less than or equal to the value programmed in the RAMUBR
and greater than or equal to the value programmed in the
RAMLBR, /RAMCS is asserted. The A18 signal from the
CPU is taken before it is multiplexed with T . In the case
OUT
that these registers are programmed to overlap,
/ROMCS takes priority over /RAMCS (/ROMCS is asserted
and /RAMCS is inactive).
Chip Select signals are going active for the address range:
Because /ROMCS takes priority over /RAMCS, the latter
will never be asserted until the value in the ROMBR and
RAMLBR registers are re-initialized to lower values.
D7 D6 D5 D4 D3 D2 D1 D0
Upon reset 1 1 1 1 1 1 1 1
A19-A12
Figure 57. ROMBR
(Z180 MPU Read/Write, Address xxE8H)
/ROMCS: (ROMBR) >= A19-A12 >= 0
/RAMCS: (RAMUBR) >= A19-A12 >= (RAMLBR)
These registers are set to FFH at POR, and the boundary
addresses of ROM and RAM are as follows:
ROM lower boundary address
(fixed) = 00000H
ROM upper boundary address
(ROMBR register) = 0FFFFFH
RAM lower boundary address
(RAMLBR register) = 0FFFFFH
ROMBR ROM Address Boundary Register
This register specifies the address range for the /ROMCS
signal. When accessed, memory addresses are less than
or equal to the value programmed in this register, the
/ROMCS signal is asserted.
The A18 signal from the CPU is obtained before it is
multiplexed with T_OUT. This signal can be forced to a “1”
(inactive state) by setting bit 3 in the System Configuration
Register, to allow the user to overlay the RAM area over the
ROM area.
RAM upper boundary address
(RAMUBR register) = 0FFFFFH
Z80182 Improvement to the Wait State Generator
A separate Wait State Generator is provided for access
memory using /ROMCS and /RAMCS. A single 8-bit register
is added to enable/disable this feature as well as provide
two 3-bit fields that provide 1 to 8 waits for each chip select.
WSG Chip Select Register (Z80182 address D8H)
There are two wait state generators in the Z182. The actual
number of wait states inserted is the greatest number of
both the Z180 WSG and the chip select WSG. In order to
use the Chip Select WSG, the Z180 WSG should be
programmed to 0 wait states.
Bit 7
/RAMCS Wait State Generator Enable.
Disable on power-up or reset.
D7 D6 D5 D4 D3 D2 D1 D0
0
0
Bits 6-4 /RAMCS Wait States 1 to 8.
Eight wait states on power-up or reset.
Bit 3
/ROMCS Wait State Generator Enable.
Disable on power-up or reset.
Bits 2-0 /ROMCS Wait States 1 to 8.
Eight wait states on power-up or reset.
/ROMCS
Wait States
1-8
/ROMCS Wait
State Generator
Enable
/RAMCS Wait
States 1-8
/RAMCS Wait State
Generator Enable
Figure 58. WSG Chip Select Register
(Z180 MPU Read/Write, Address xxD8H)
3-60
DS971820600