Zilog Z86193 - Manual (Page 19)

Z8
®
CPU
User Manual
UM001604-0108 Address Space
12
When an ERF Bank is selected, register addresses
00h
to
0Fh
access those sixteen ERF
Bank registers—in effect replacing the first sixteen locations of the Z8
®
Standard Register
File.
For example, if ERF Bank C is selected, the Z8 Standard Registers
00h
through
0Fh
are
no longer accessible. Registers
00h
through
0Fh
are now the 16 registers from ERF Bank
C, Working Register Group 0. No other Z8 Standard Registers are affected because only
Working Register Group 0 is implemented in ERF Bank C.
Access to the ERF is accomplished through the Register Pointer (
FDh
). The lower nibble
of the Register Pointer determines the ERF Bank while the upper nibble determines the
Working Register Group within the register file, as displayed in
Figure 7 .
The value of the lower nibble in the Register Pointer (
FDh
) corresponds to the ERF Bank
identification. Table 4 lists the lower nibble value and the register file assigned to it.
Figure 7. Register Pointer Example
Table 4. ERF Bank Address
Register Pointer
(FDh) Low Nibble
Hex Register File
0000b 0 Z8 Standard Register File*
0001b 1 Expanded Register File Bank 1
0010b 2 Expanded Register File Bank 2
0011b 3 Expanded Register File Bank 3
0100b 4 Expanded Register File Bank 4
0101b 5 Expanded Register File Bank 5
0110b 6 Expanded Register File Bank 6
0111b 7 Expanded Register File Bank 7
1000b 8 Expanded Register File Bank 8
0 1 1 1 1 1 0 0
Working
Select ERF Bank Ch
Register
Group
Expanded
Register
Bank
Working Register Group 7h