NEC PD17062 - Manual (Page 247)

247
µ
PD17062
Fig. 20-2 VRAM Data Configuration
20.4.1 ID Field
The ID field indicates the type of data in the data field.
The data field can hold the following three types of data.
(1) Character pattern select data
(2) Carriage return data
(3) Control data select data
Table 20-3 ID Field
20.4.2 Character Pattern Select Data
The character pattern is the data of an image displayed on a screen such as a TV screen. It is allocated
in the CROM area (at 0800H to 0F7FH) of program memory. The character pattern select data becomes part
(b
9
to b
4
) of a CROM address. In other words, the 6 bits of data in the data field indicate b
9
to b
4
of the CROM
address.
CROM consists of BANK0 and BANK1. Note that even if the 6-bit VRAM data is the same, the CROM address
varies according to the value of the CROMBNK (b
0
at 30H). If the data field contains a value of 0 (000000B),
the CROM address is 080
×
H (10000000
ЧЧЧЧ
B) or 0C0
×
H (11000000
ЧЧЧЧ
B). Specifying the BANK of CROM
selects 080
×
H or 0C0
×
H. Table 20-4 lists the CROM addresses that the VRAM character pattern select data
actually points to.
b
7
b
6
b
5
b
4
b
3
b
2
b
1
b
0
(b
3
) (b
2
) (b
1
) (b
0
) (b
3
) (b
2
) (b
1
) (b
0
)
ID field Data field
Even address Odd address
ID field
Type of data in the data field
b 7 b 6
0 0 Character pattern select data
0 1 Carriage return (return address) to BANK1 (from BANK1 to
BANK1, and from BANK2 to BANK1)
1 0 Control data
1 1 Carriage return (return address) to BANK2 (from BANK2 to
BANK2)