The RAM.Bo256 Project Page

A RAM Add-On Board for the HCS12

About RAM.Bo256

RAM.Bo256 RAM Add-On Board

RAM.Bo256 is a RAM Add-On Board for the HCS12 Microcontrollers. It provides 256KB of RAM for easy debugging and code download. The schematic diagram, circuit description and necessary software will be published on this project page.

RAM.Bo256 on HCS12 T-Board

It can be plugged directly onto a DP256 "Barracuda" EVB (Motorola) or a HCS12 T-Board (Elektronikladen) as shown in the picture above.

Schematic Diagram

RAM.Bo256 V1.1 Schematic Diagram

RAM.Bo256 V1.1 Schematic Diagram (click image to enlarge)

Schematic Diagram PDF Version (142KB)

Enhanced Version Schematic V1.3

RAM.Bo256 V1.3 Schematic Diagram

RAM.Bo256 V1.3 Schematic Diagram (click image to enlarge)

Some features were added with the introduction of Enhanced Version V1.3 starting April 2004. When using default settings the new version behaves exactly the same way as V1.1.

System Initialization

In order to access the external RAM, the HCS12 must be initialized properly. The following script file shows how this can be accomplished using the NoICE Remote Debugger.

First, the debugger will issue a reset and the MCU will start in Single Chip Mode. After that, the debugger must perform a number of control register accesses, as detailed below. As a result, the Multiplexed External Bus Interface is prepared to access the RAM.Bo256 ressources.

The final step is to switch over to Expanded Mode by accessing the MODE register. The MCU will then "see" the external RAM in the address range $4000..$7FFF. Specific portions (pages) of the external RAM can be selected by setting PORTK. Since one page is 16KB, the total number of pages is 16 (16x16KB=256KB).

ECHO ----------------------------------------------------------------
ECHO Initialization Command File for RAM.Bo256 RAM Add-On Board
ECHO on Elektronikladen HCS12 T-Board or Motorola Barracuda EVB,
ECHO external RAM can be accessed in the window 0x4000..0x7FFF
ECHO ----------------------------------------------------------------
ECHO http://hc12web.de/rambo256/
ECHO ----------------------------------------------------------------

REM +-------+
REM | PORTK | all H
REM +-------+
EDIT 0x0032 0xFF
REM +----- -+
REM | DDRK  | all output
REM +-------+
EDIT 0x0033 0xFF
REM +----- -+
REM | MISC  | set ROMHM (keep ROMON)
REM +-------+
EDIT 0x0013 0x03
REM +----- -+
REM | PEAR  | enable /LSTR and R/W, stretch=0
REM +-------+
EDIT 0x000A 0x0C
REM +----- -+
REM | MODE  | Normal Expanded Wide Mode
REM +-------+
EDIT 0x000B 0xE0

About the Author, Copyright stuff

The RAM.Bo256 project is Copyright by

Oliver Thamm
Leipzig, Germany

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