Maxim Integrated DS4830A Optical Microcontroller - Manual (Page 15)

DS4830A User’s Guide
15
the source data will be equal to the prefix data as the upper 8 bits and 00h as the lower 8 bits. If the source is
from a module containing only 16-bit source registers, 0000h source data is used for the transfer.
Table 2-1. Register-to-Register Transfer Operations
SOURCE REGISTER
SIZE (BITS)
DESTINATION REGISTER SIZE
(BITS)
PREFIX
SET?
DESTINATION SET TO VALUE
HIGH 8 BITS LOW 8 BITS
8 8 X — Source [7:0]
8 16 No 00h Source [7:0]
8 16 Yes PFX [7:0] Source [7:0]
16 8 X — Source [7:0]
16 16 X Source [15:8] Source [7:0]
2.3 – Memory Types
In addition to the internal register space, the DS4830A incorporates the following memory types:
• 32KWords of flash memory
• 4KWords of utility ROM contain a debugger and program loader
• 2KWords of SRAM
• 32-level hardware stack for storage of program return addresses
The memory on the DS4830A is organized according to Harvard architecture. This means that there are separate busses
for both program and data memory. Stack memory is also separate and is accessed through a dedicated register set.
2.3.1 – Flash Memory
The DS4830A contains 32KWords (32K x 16) of flash memory. The flash memory begins at address 0000h and is
contiguous through word address 7FFFh. The flash memory can also be used for storing lookup tables and other non-
volatile data.
The incorporation of flash memory allows the contents of the flash memory to be upgraded in the field, either by the
application or by one of the bootloaders (JTAG or I
2
C). Writing to flash memory must be done indirectly by using routines
that are provided by the utility ROM. See the Utility ROM and In-System Programming sections for more details.
2.3.2 – SRAM Memory
The DS4830A contains 2KWords (2K x 16) of SRAM memory. The SRAM memory address begins at address 0000h and
is contiguous through word address 07FFh. The contents of the SRAM are indeterminate after power-on reset, but are
maintained during non-POR resets.
When using the in-circuit debugging features, the highest 19 bytes of the SRAM must be reserved for saved state storage
and working space for the debugging routines. If in-circuit debug is not used, the entire 2KWords of SRAM is available for
application use.
2.3.3 – Utility ROM
The utility ROM is a 4kWord segment of memory. The utility ROM memory address begins at word address 8000h and is
contiguous through word address 8FFFh. The utility ROM is programmed at the factory and cannot be modified. The
utility ROM provides the following system utility functions:
• Reset vector (not user code reset vector)
• In-system programming (bootstrap loader) over JTAG or I 2
C-compatible interfaces
• In-circuit debug routines
• Routines for in-application flash programming
Following any reset, the DS4830A automatically starts execution at the Reset Vector which is address 8000h in the utility
ROM. The ROM code determines whether the program execution should immediately jump to the start of application code
(flash address 0000h), or to one of the special routines mentioned. Routines within the utility ROM are firmware-
accessible and can be called as subroutines by the application software. See the Utility ROM, In-System Programming,
and In-Circuit Debug sections for more information on the routines provided by the utility ROM.