38K0 Datasheet, PDF (70/133 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

38K0 Group
MULTICHANNEL RAM
The 38K0 group has the built-in multichannel RAM including the
small logic circuit (RAM I/F) instead of ordinary RAM.
The multichannel RAM has the USB channel and the EXB channel
in addition to the CPU channel.
The multichannel RAM controls access from CPU, USB and EXB,
synchronizing control with φ. The USB transfer rate is about 1.5
Mbytes/second. Access to the multichannel RAM is performed at
every about 5.3 clocks in φ = 8 MHz, or at every about 4 clocks in
φ = 6 MHz. The USB’s access has priority to the EXB’s.
The one wait function (ONW function) of 38000 series CPU is
used internally to control access with the CPU. When receiving an
access request from the USB or the EXB, the multichannel RAM
outputs ONW signal to wait the CPU for one clock, and access of
the USB or the EXB is performed.
If the multichannel RAM is outputting ONW signal while the CPU
is in the state of reading/writing for the RAM area, the CPU read
cycle or write cycle is extended by 1 period of φ.
No wait
ONW = “H”
No wait
Except RAM
No wait
No RD/WR
CPU bus cycle
φ
CPU AD
RD/WR
Multichannel RAM
USB REQ
EXB REQ
ONW
RAM bus cycle
RAM access right
RAM RD/WR
RAM area
Except RAM
RAM area
CPU
USB
CPU
Fig. 99 Multichannel RAM timing diagram (no wait)
CPU bus cycle
φ
CPU AD
RD/WR
Multichannel RAM
USB REQ
EXB REQ
ONW
RAM bus cycle
RAM access right
RAM RD/WR
One wait
CPU accessing RAM at the latter part
Prior CPU
One wait
Prohibiting continuous access of
USB/EXB
Prior CPU
One wait
USB having priority of USB/EXB
simultaneous access
Prior USB
Prior CPU
RAM area
RAM area
RAM area
One wait
2-cycle wait (max.) for EXB
RAM area
EXB
CPU
USB
CPU
USB
CPU
EXB
CPU
Fig. 100 Multichannel RAM timing diagram (one wait)
Rev.3.00 Oct 05, 2006 page 70 of 129
REJ03B0192-0300