Hardware manual

Rev. 3.0, 09/98, page 251 of 361
Section 14 ROM
14.1 Overview
The H8/338 includes 48k bytes of high-speed, on-chip ROM. The H8/337 has 32k bytes. The
H8/336 has 24k bytes. The on-chip ROM is connected to the CPU via a 16-bit data bus. Both
byte data and word data are accessed in two states, enabling rapid data transfer and instruction
fetching.
The on-chip ROM is enabled or disabled depending on the MCU operating mode, which is
determined by the inputs at the mode pins (MD
1
and MD
0
). See table 14.1.
Table 14.1 On-Chip ROM Usage in Each MCU Mode
Mode Pins
Mode MD
1
MD
0
On-chip ROM
Mode 1 (expanded mode) 0 1 Disabled (external addresses)
Mode 2 (expanded mode) 1 0 Enabled
Mode 3 (single-chip mode) 1 1 Enabled
The H8/338 and H8/337 are available with electrically programmable ROM (PROM), or with
masked ROM. The PROM version has a PROM mode in which the chip can be programmed with
a standard PROM writer.