SMS24 datasheet(12/18 Pages) SUMMIT

12 / 18 page

SMS24

2048 2.4. 3/1/01

SUMMIT MICROELECTRONICS, Inc.

IN-SYSTEM PROGRAMMING THE SMS24

The need for an in-system programming interface for a

supervisory circuit is necessitated by the rapid change to

both board designs (feature upgrades to a common de-

sign core) and the ICs resident on the boards. The SMS24

provides an ideal solution for maintaining currency with

the change in boards and their power supplies as they shift

from generation to generation.

Theory of Operation

The SMS24 can be designed-in with the simple addition of

an inexpensive 9-pin 0.100” centerline header. Summit

supports this configuration with the SMX3199-A program-

mer, and in the future will support this interface with the

SMX3200. Depending upon the end use of the interface,

prototyping vs. field support, the header can be placed

anywhere on the board or as a right angle header at the

back edge of the card (the side pointing outwards from a

card cage).

The basic interface circuit is shown in Figure 3. In order

to clearly illustrate the examples, all additional traces and

series resistors are either bold or outlined in a dashed box.

Notes:

If the device appears to be ignoring attempts to be

programmed ensure the supplied VCC is above the

programmed threshold. If VCC is below the reset

threshold all attempts to write to the device will be

ignored.

If you are writing to the memory array and ‘read-

backs’ show occasional rows not being written check

the watchdog timer. Either disable the watchdog or

insure WDI is being strobed (high to low) at intervals

less than the programmed watchdog time out period.

Figure 3 is a block diagram illustration of the SMS24

configured as device code 110. The comments in bold

italics indicate the programmable options for this code

Supporting the SMS24 is a programming module, the

SMX3199-A. The hardware is a small printed circuit card

that interfaces to a standard PC parallel printer port. A

target programming cable is connected from this to the

user’s card. The software provides an intuitive configura-

tion screen and also a memory test verification screen

(examples of the screens are shown).

SCL

SDA

VLOW#

VCC

WDI

RST#

VSENSE

GND

Device code 110

WDI

SCL

SDA

Board WDI in

Board Serial Bus

Ω

10k

Ω

10k

Ω

100k

Ω

2046 Fig03 2.0

Board

RST#

Board

VSENSEIN

Figure 3. Basic Interface Circuit

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