Hardware manual

Rev. 3.0, 09/98, page 249 of 361
Section 13 RAM
13.1 Overview
The H8/338 includes 2k bytes of on-chip static RAM. The H8/337 and H8/336 have 1k byte. The
RAM is connected to the CPU by a 16-bit data bus. Both byte and word access to the on-chip
RAM are performed in two states, enabling rapid data transfer and instruction execution.
The on-chip RAM is assigned to addresses H'F780 to H'FF7F in the address space of the H8/338,
and addresses H'FB80 to H'FF7F in the address space of the H8/337 and H8/336. The RAME bit
in the system control register (SYSCR) can enable or disable the on-chip RAM, permitting these
addresses to be allocated to external memory instead, if so desired.
13.2 Block Diagram
Figure 13.1 is a block diagram of the on-chip RAM.
Internal data bus (upper 8 bits)
Internal data bus (lower 8 bits)
Even address Odd address
H'F780
H'F782
H'FF7E
H'F781
H'F783
H'FF7F
On-chip RAM
Figure 13.1 Block Diagram of On-Chip RAM (H8/338)