Sharp ER-A750 Service Manual page 61

1 Output address change
The ER-A750 uses the expansion RAM board at the RAS3 area and
its high-order IMB space (200000h
Basically, the ER-03MB is supposed to be used in the area from
300000h 7FFFFFh; the ER-04MB in the area from 700000h
8FFFFFh. Therefore, it is necessary to convert the addresses as
shown below.
ER-A750
200000H
300000H
400000H
<Address conversion table>
Address A23
2XXXXXh 0
3XXXXXh 0
4XXXXXh 0
5XXXXXh 0
ER-03/04MB
Address RA23
7XXXXXh 0
8XXXXXh 1
9XXXXXh 1
AXXXXXh 1
In the tables, the address 400000h and after at the side of the ER-
A750 are not used by the ER-03MB or ER-04MB, but is kept consid-
ering the commercialization of 4 Mb of expansion RAM in future.
The ER-03MB and ER-04MB use RA21 and RA20, respectively, be-
cause they do not have RA23 or RA22.
The address conversion circuit of RA21 and RA20 is shown below.
A21
A20
2 Decode base signal change
As decode signals, RAS3E and RAS30 signals are generated for even
and odd addresses, respectively, based on the RAS3 signal
(200000h 3FFFFFh). To allocate even and odd addresses, the ad-
dress line A0 is used.
3FFFFFh).
ER-03MB
ER-04MB
700000H
800000H
900000H
Fig. 12
Table 16
ER-A750
A22 A21
0 1
0 1
1 0
1 0
RA22 RA21
1 1
0 0
0 0
0 1
RA21
RA20
Fig. 13
13-2. Terminal table
The terminal table of the RAM connector is shown below.
<Expansion RAM connector terminal table>
Signal name
GND
GND
RA21
PSX (Open)
+5V
VCKDC
VRAM
A16
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
A18
A20
D0
0
D1
1
D2
0
RESET
1
GND
GND
* The signals in ( ) are not used.
RA20
1
0
1
0
7 – 31
Table 17
Pin No. Pin No.
1 2
3 4
5 6
7 8
9 10
11 12
13 14
15 16
17 18
19 20
21 22
23 24
25 26
27 28
29 30
31 32
33 34
35 36
37 38
39 40
41 42
43 44
45 46
47 48
49 50
Signal name
GND
GND
RA20
PRAS30
+5V
VCKDC
VRAM
A15
WR
A13
A8
A9
A11
PSREF
A10
A17
A19
PRAS3E
D7
D6
D5
D4
D3
GND
GND