m37905 Renesas Electronics Corporation., m37905 Datasheet - Page 35

• Manufacturer Part Number: m37905
• Description: Mitsubishi 16-bit Single-chip Microcomputer 7700 Family / 7900 Series
• Manufacturer: Renesas Electronics Corporation.

Internal ROM bus cycle select bit: Bit 7 at address 5F
Note: We usually recommend to select “bus cycle = 2 .” When reprogramming the internal flash memory
CENTRAL PROCESSING UNIT (CPU)
2.2 Bus interface unit (BIU)
Table 2.2.4 Bus cycles at access to internal area
2-12
ROM
RAM
2.2.2 Data Transfer (read and write)
When the CPU reads or writes data from or to the internal area, it requests the BIU to read or write data.
The BIU outputs control signals in order to control the internal address and data buses in response to the
request from the CPU. The cycle where the following are performed is referred to “bus cycle”:
• The BIU controls buses.
• Data transfer is performed between the internal area and BIU.
Table 2.2.4 lists the bus cycles at access to the internal area. Figure 2.2.4 shows operating waveform
examples at reading from or writing to the internal area.
SFR
(1) Reading data
(2) Writing data
in the CPU reprogramming mode, be sure to select bus cycle = 3 . (Refer to section “19.2 Flash
memory CPU reprogramming mode.”)
so the CPU requests the data. In this case, the CPU waits until the requested data is ready in the
BIU.
reads the contents of the informed address and takes them into the data buffer. The CPU continues
processing using data in the data buffer.
so the CPU writes the data into the data buffer. The BIU outputs the address informed by the CPU
onto the internal address bus. Then, the BIU writes the data in the data buffer into the informed
address.
The CPU informs the BIU’s data address register of the address where the data to be read is stored,
The BIU outputs the address informed by the CPU onto the internal address bus. Then, the CPU
The CPU informs the BIU’s data address register of the address to which the data will be written,
Internal address bus
Internal data bus
(Internal ROM bus cycle select bit = 0)
Bus cycle = 3 (Note)
BIU
Address
1 bus cycle = 3
Internal address bus
7905 Group User’s Manual Rev.1.0
Internal data bus
Data
BIU
16
1 bus cycle = 2
Address
Internal address bus
Internal data bus
(Internal ROM bus cycle select bit = 1)
Data
Bus cycle = 2 (Note)
BIU
1 bus cycle = 2
Address
Data