6V7 Datasheet, PDF (29/298 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER with CLOSED CAPTION DECODER and ON-SCREEN DISPLAY CONTROLLER

M306V7MG/MH/MJ/MJA-XXXFP, M306V7FG/FH/FJ/FJAFP
2.4.4 Bus Control
The following explains the signals required for accessing external devices. The signals required for ac-
cessing the external devices are valid when the processor mode is set to memory expansion mode and
microprocessor mode.
(1) Address bus/data bus
The address bus consists of the 20 pins A0 to A19 for accessing the 1M bytes of address space.
The data bus consists of the pins for data I/O. When the BYTE pin is “H”, the 8 ports D0 to D7 function
as the data bus. When BYTE is “L”, the 16 ports D0 to D15 function as the data bus.
When a change is made from single-chip mode to memory expansion mode, the value of the address
bus is undefined until external memory is accessed.
(2) Chip select signal
The chip select signal is output using the same pins as P4 to P47. Bits 0 to 3 of the chip select control
register (address 000816) set each pin to function as a port or to output the chip select signal. The chip
select control register is valid in memory expansion mode and microprocessor mode. In single-chip
mode, P44 to P47 function as programmable I/O ports regardless of the value in the chip select control
register.
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In microprocessor mode, only CS0 outputs the chip select signal after the reset state has been can-
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celled. CS1 to CS3 function as input ports. Figure 2.4.4 shows the chip select control register.
The chip select signal can be used to split the external area into as many as four blocks. Table 2.4.3
shows the external memory areas specified using the chip select signal.
Table 2.4.3 External areas specified by the chip select signals
Chip select
CS0
CS1
CS2
CS3
Memory expansion mode
1800016 to 3FFFF16 (160K)
1000016 to 17FFF16 (32K)
0C00016 to 0FFFF16 (16K)
0800016 to 0BFFF16 (16K)
Specified address range
Microprocessor mode
1800016 to 3FFFF16 (160K), 6000016 to FFFFF16 (640K)
1000016 to 17FFF16 (32K)
0C00016 to 0FFFF16 (16K)
0800016 to 0BFFF16 (16K)
Rev.1.00 May 18, 2004 page 29 of 296