Propeller Manual

Introducing the Propeller Chip
Boot Up Procedure
Upon power-up (+ 100 ms), RESn low-to-high, or software reset:
1. The Propeller chip starts its internal clock in slow mode (≈ 20 kHz), delays for 50 ms
(reset delay), switches the internal clock to fast mode (≈ 12 MHz), and then loads and
runs the built-in Boot Loader program in the first processor (Cog 0).
2. The Boot Loader performs one or more of the following tasks, in order:
a. Detects communication from a host, such as a PC, on pins P30 and P31. If
communication from a host is detected, the Boot Loader converses with the
host to identify the Propeller chip and possibly download a program into
Main RAM and optionally into an external 32 KB EEPROM.
b. If no host communication was detected, the Boot Loader looks for an
external 32 KB EEPROM (24LC256) on pins P28 and P29. If an EEPROM
is detected, the entire 32 KB data image is loaded into the Propeller chip’s
Main RAM.
c. If no EEPROM was detected, the boot loader stops, Cog 0 is terminated, the
Propeller chip goes into shutdown mode, and all I/O pins are set to inputs.
3. If either step 2a or 2b was successful in loading a program into the Main RAM, and a
suspend command was not given by the host, then Cog 0 is reloaded with the built-in
Spin Interpreter and the user code is run from Main RAM.
Run-Time Procedure
A Propeller Application is a user program compiled into its binary form and downloaded to
the Propeller chip’s RAM and, possibly, external EEPROM. The application consists of code
written in the Propeller chip’s Spin language (high-level code) with optional Propeller
Assembly language components (low-level code). Code written in the Spin language is
interpreted during run time by a cog running the Spin Interpreter while code written in
Propeller Assembly is run in its pure form directly by a cog. Every Propeller Application
consists of at least a little Spin code and may actually be written entirely in Spin or with
various amounts of Spin and assembly. The Propeller chip’s Spin Interpreter is started in
Step 3 of the Boot Up Procedure, above, to get the application running.
Once the boot-up procedure is complete and an application is running in Cog 0, all further
activity is defined by the application itself. The application has complete control over things
like the internal clock speed, I/O pin usage, configuration registers, and when, what and how
Page 18 · Propeller Manual v1.1