UPD784026 Renesas Electronics Corporation., UPD784026 Datasheet - Page 625

• Manufacturer Part Number: UPD784026
• Description: 16/8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

21.2 WAIT FUNCTION
access cycle.
the access time.
21.2.1 Wait Function Control Registers
(1) Memory extension mode register (MM)
When a low-speed memory or I/O is connected externally to the PD784026, waits can be inserted in the external memory
There are two kinds of wait cycle, an address wait for securing the address decoding time, and an access wait for securing
The IFCH bit of the MM performs wait control setting for internal ROM accesses, and the AW bit performs address
wait setting.
The MM can be read or written to with an 8-bit manipulation instruction. The MM format is shown in Figure 21-8.
When RESET is input, the MM register is set to 20H, the same cycle as for external memory is used for internal ROM
accesses, and the address wait function is validated.
MM
IFCH
7
6
0
Figure 21-8 Memory Extension Mode Register (MM) Format
AW
5
CHAPTER 21 LOCAL BUS INTERFACE FUNCTION
4
0
MM3
3
MM2
2
MM1
1
MM0
0
Memory extension mode settings (see 21.1
MEMORY EXTENSION FUNCTION)
IFCH
0FFC4H
Address
AW
0
1
0
1
Address Wait Specification
Disabled
Enabled
Internal ROM Fetches
Fetch performed at same speed as
external memory
All wait control settings valid
High-speed fetches performed
Wait control specification invalid
On Reset
20H
R/W
R/W
585