MB

91191/192 Series

13

(Bus names)

• I bus : 16-bit bus for internal instructions. As the FR family of CPUs use the Harvard architecture, instructions

and data use separate buses. A bus converter is connected to the I bus.

• D bus : Internal 32-bit data bus. The internal peripherals are connected to the D bus.

• C bus : Internal multiplexed bus. Connected to the I and D buses via a switch. An external interface module

is connected to the C bus. Data and instructions are multiplexed on the external data bus.

• R bus : Internal 16-bit data bus. The R bus connects to the D bus via an adapter. The I/O, clock oscillator, and

interrupt controller are connected to the R bus. As the R bus is only 16 bits wide, address and data

are multiplexed on the bus and therefore multiple cycles are required when the CPU accesses these

resources.