diff --git a/README.md b/README.md
index 8ac1e970..636d6931 100644
--- a/README.md
+++ b/README.md
@@ -258,11 +258,13 @@ Each expander can support up to 32 GPIO. To use an expander for buttons, an inte
 
 The parameter "gpio_exp_config" is a semicolon (;) separated list with following syntax for each expander
 ```
-model=<model>,addr=<addr>,[,port=system|dac][,base=<n>|100][,count=<n>|16][,intr=<gpio>]
+model=<model>,addr=<addr>,[,port=system|dac][,base=<n>|100][,count=<n>|16][,intr=<gpio>][,cs=<gpio>][,speed=<Hz>]
 ```	
-- model: pca9535, pca85xx (untested) and mcp23017
-- addr: inthe i2c address decimal 	
-- port: use either "system" port (shared with display for example) or "dac" port (system is default)
+- model: pca9535, pca85xx (untested), mcp23017 and mcp23s17 (SPI version, untested)
+- addr: chip i2c/spi address (decimal)
+- port (I2C): use either "system" port (shared with display for example) or "dac" port (system is default)
+- cs (SPI): gpio used for Chip Select
+- speed (SPI): speed of the SPI bus for that device (in Hz)	
 - base: GPIO numbering offset to use everywhere else (default 40)
 - count: number of GPIO of expander (default 16 - might be obsolted if model if sufficient to decide)
 - intr: real GPIO to use as interrupt.