ez80190 ZiLOG Semiconductor, ez80190 Datasheet - Page 63

• Manufacturer Part Number: ez80190
• Description: Ez80190 Microprocessor
• Manufacturer: ZiLOG Semiconductor

Chip Selects and Wait States
PS006613-0306
Memory and I/O Chip Selects
Memory Chip Select Operation
The eZ80190 device generates four Chip Selects for external devices. Each Chip
Select may be programmed to access either memory space or I/O space. The
Memory Chip Selects can be individually programmed on a 64 KB boundary. The
I/O Chip Selects can each choose a 16-byte section of I/O space. In addition,
each Chip Select may be programmed for up to 7 WAIT states.
Each of the 4 available Chip Selects can be enabled for either the memory
address space or the I/O address space, but not both. To select the memory
address space for a particular Chip Select, CS_IO (CSx_CTL[4]) must be reset to
0. To select the I/O address space for a particular Chip Select, CS_IO must be set
to 1. After RESET, the default is for all Chip Selects to be configured for the mem-
ory address space. For either the memory address space or the I/O address
space, the individual Chip Selects must be enabled by setting CS_EN
(CSx_CTL[3]) to 1.
Each of the 4 Memory Chip Selects features 3 control registers. To enable a par-
ticular Memory Chip Select, the following conditions must be met:
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If all of the foregoing conditions are met to generate a Memory Chip Select, then
the following actions occur:
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The Chip Select is enabled by setting CS_EN to 1
The Chip Select is configured for memory by clearing CS_IO to 0
The address is in the associated Chip Select range:
CSx_LBR[7:0] ≤ ADDR[23:16] ≤ CSx_UBR[7:0]
No higher priority (lower number) Chip Select meets the above 3 conditions
No on-chip RAM is configured for the same address space, because on-chip
RAM is prioritized higher than all Memory Chip Selects
A memory access instruction must be executing
A Chip Select—CS0, CS1, CS2, or CS3—is activated (driven Low)
The MREQ signal is activated (driven Low)
PRELIMINARY
eZ80190 Product Specification
Chip Selects and Wait States
49