Serial Peripheral Interface(SPI)

SPI是一種界面技術，該界面可以用來連接Flash device 與 ICH，是目前主流的BIOS flash chip的技術，在這之前的技術是Firmware Hub over LPC bus。以下是節錄自Intel ICH7規格書的ㄧ句話清楚的道出什麼SPI:

The Serial Peripheral Interface (SPI) is a 4-pin interface that provides a potentially
lower-cost alternative for system flash versus the Firmware Hub on the LPC bus.

Communication on the SPI bus is done with a Master – Slave protocol. The typical bus
topology consists of a single SPI Master (ICH7) with a single SPI Slave (flash device).
The Slave is connected to the ICH7 and is implemented as a tri-state bus.

When SPI is selected by the Boot BIOS Destination Strap and a SPI device is detected
by the ICH7, LPC based BIOS flash is disabled.


從以前到現在BIOS flash chip的技術演進；
1. Flash memory device over ISA
2. Firmware Hub chip with flash memory device over LPC
3. Flash memory devivce over SPI


參考；

http://en.wikipedia.org/wiki/BIOS


以下的內容節錄自:

www.electro-tech-online.com/general-electronics-chat/35857-lpc-fwh-spi-used-bios-rom.html



1. Are they used only in BIOS ROM? Where can we also see them?
2. In what situation do we use these terms?
3. What are these features respectively?


These terms are used on PC/x86 motherboards.
LPC = low pin count interface (basically replaced the legacy ISA bus stuff)
FWH = firmware hub (a chip/hub used to store the BIOS codes)
SPI = serial flash chip using the SPI bus/interface (basically a FWH with less pins)



1. LPC is usually part of the south bridge or ICH (I/O control hub), and the FWH and SPI are related to the BIOS ROM.

2. We use these terms/alphabets when discussing the BIOS, hubs/chips or busses related to an x86 motherboard.

3. LPC is a bus (or a port) that other circuits/chips can connect to on a motherboard. For example the PS/2 type keyboard & mouse ports (along with a few other I/O functions) are connected to an LPC-type chip which connects to the LPC port on the ICH. FWH are SPI are typically thought of as chips (some insist it's a hub). This is used to store the BIOS firmware/codes. For example, the Phoenix/Award BIOS or AMI BIOS (or other equivalent BIOS) codes are stored in this FWH or SPI serial chip.


Sometimes we can recognize an FWH and SPI chip, but not the LPC item (but it's there).

The brand on the FWH is typically SST, Atmel, Intel or Winbond. However with the Winbond brand we'll have to be careful as they make many other types of chips too (not just memory chips - but their other chips typically have a lot of pins, ie. more than 32 for a FWH). The FWH is usually a 32-pin PLCC chip. Most/some of the time it'll be sitting in a socket so that it's removable if anybody wants to do this. It'll typically have a 29-something part number.

If we can't find a 32-pin FWH (PLCC chip with or without socket), then we'll have to look for an 8-pin chip of those similar brands. The part number is typically 25-something or 45-something, etc. The SPI chip is normally 8-pin, and it is sometimes found on recent motherboards using the Intel 965 or newer chipsets. It is normally soldered down - without a socket.

1. Can we regard 32-pin PLCC as BIOS rom?
2. When it comes to motherboard design, what kind of chips are connected to
LPC/FWH/SPI?
3. In contrast to LPC, what is HPC(high pin count) used for?

Hey there.
1. Yes we can regard the 32-pin PLCC as a BIOS ROM chip but this as long as it's a memory/flash/EE type of chip.

2a. It's usually the south bridge chip (I/O controller hub) where the BIOS chip (LPC/FWH/SPI) connects to, ie. it's like a leaf of its own and hanging off this south bridge branch. From the south bridge chip, various other items connect to/out from here.

2b. As for the LPC bus itself, some items such as the BIOS chip, Super I/O (multifunction) chip, optional TPM/security chip, and other ~low-speed/bandwidth chips can be found here.

3a. We normally don't hear anything called HPC (high pin count) on a motherboard but there are various chips with lots of pins. There's HPC for a high-performance something-else though.

3b. It's usually in the microcontroller world (for example, the PIC stuff) where we find this HPC term. It's because the PIC originally came with a few pins and over the years they added many more general-purpose I/O pins.