diff --git a/NI_PCI6602.md b/NI_PCI6602.md
index 9fe8eb8..d917f5b 100644
--- a/NI_PCI6602.md
+++ b/NI_PCI6602.md
@@ -1,3 +1,13 @@
 # Overview
 
-The basic functions of Pixelator are implemented on the [NI PCI6602](https://www.ni.com/docs/en-US/bundle/ni-660x-specs/resource/372141b.pdf) card. 
\ No newline at end of file
+The basic functions of Pixelator are implemented on the [NI PCI6602](https://www.ni.com/docs/en-US/bundle/ni-660x-specs/resource/372141b.pdf) Counter/Timer card. (In future, other options will be implemented that avoid NI cards altogether.)
+
+The NI PCI6602 card provides the clock that governs the measurement dwell time and triggers detectors, often referred to as the "pixel clock". These are constructed from the first 3 subdevices (of 8 total) using the following external connections.
+
+
+| Function | Header | Header |
+| --- | --- | --- |
+| <colspan=2>Cell | 3 | C0 Gate |
+| Cell | 8 | C2 Out |
+| Cell | Cell | Cell |
+