Hitachi AP1 Data Book page 93

--------------------------------------------------------HMCS46C,HMCS46CL
• Designation of ROM Address and ROM Code
The bank part of the ROM address is shown in the binary
system and the page part in the decimal system. The address
part is divided into 2 bits and 4 bits, and shown in the hexa-
decimal system.
It is possible to combine the bank part and the page part and
show the combined part as the Page (in the decimal system).
(a) ROM Address
; - - - - (Page Part!
~
Bank Part
In this case, the 0 Page to the 31 Page in the Bank 1 are shown
as the 32 Page to the 63 Page. The examples are 'shown in Figure
3.
One word (10 bits) of ROM is divided into three parts (2
bits, 4 bits and 4 bits from the most significant bit 010 in order)
shown in the hexa-decimal system. The examples are shown in
Figure 3.
/ \ r -
Page Part----.'
~Address Part~
1 1 1 1 : ° : 1 : ° : ° 1 : 0 : 0 : 1 : 1 : ° 1
Bank 1 20-26: Bank 1 20 Page 26 Address
(52-26: 52 Page 26 Address)
'---.I~
Decimal ------1''-----.1 ' - - - - Hexa-
~
Binary
He~a-
decimal
~---(Decimal)
_ _ _
~I
decImal
(b) ROM Code
°'0
_0,
° : 1 : 1 : ° : 1 : ° : 1
I
ROM Pattern, Object Code: 1B5
L Hexa-
-1'---
Hexa-decimal
~'----
Hexa-decimal---1
decimal
Figure 3 Designation of ROM Address and ROM Code
• PATTERN GENERATION
The pattern (constant) can be accessed by the pattern in-
struction (P). The pattern can be written in any address of the
ROM address space_
• Reference
ROM addressing for reference of the patterns is achieved by
modifying the program counter with the accumulator, the B
register, the Carry F/F and the operand p. Figure 4 shows how
to modify the program counter_The address part is replaced
with the accumulator and the lower 2 bits of B register, while
the page part and the bank part are ORed with the upper 2 bits
of B register, the Carry F /F and the operand p.
The value of the operand p (P2 , PI, Po) is 0 to 7 (decimal).
The bank part of the ROM address to be referenced to is
determined by the logical equation: PC
ll
+ P2 (P2
= the MSB of
the operand p).
If
the address where the pattern instruction exists is in the
Bank 1, only the pattern of the Bank 1 can be referenced.
If
the address where the pattern instruction exists is in the
Bank 0, the pattern of the either Bank 1 or Bank 0 can be refer-
enced depending on the value of
P2.
The truth table of the bank
part of the ROM address is shown in Table 2.
The value of the program counter is apparently modified and
does not change actually. After execution of the pattern instruc-
tion, the program counter counts up and the next instruction is
91
executed.
The pattern instruction is executed in 2-cycle time.
• Generation
The pattern of referred ROM address is generated as the fol-
lOwing two ways:
(i) The pattern is loaded into the accumulator and B
register.
(li) The pattern is loaded into the Data I/O Registers R2
and R3.
Selection is determined by the command bits (0
9 ,
010) in
the pattern.
Mode (i) is performed when
0
9
is "1" and mode (ii) is per-
formed when 010 is "1 ".
Mode (i) and (ii) are simultaneously performed when both of
0
9
and 010 are "1". The correspondence of each bit of the pat-
tern is shown in Figure 5.
Examples of the pattern instruction usage is shown in Table
3_
CAUTION
In the program execution, the pattern can not be distinguish-
ed from the instruction. When the program is executed at the
addresses into which pattern is written, the instruction corres-
ponding to the pattern bit is executed_ Take care that a pattern
is not executed as an instruction.