From bbea5ce1974e00d675875854691c049c079ab188 Mon Sep 17 00:00:00 2001
From: Peter Hinch <peter@hinch.me.uk>
Date: Tue, 26 Aug 2025 14:51:42 +0100
Subject: [PATCH] RP2.md, SPI master: Add note re CS/ pull-up.

---
 rp2/RP2.md | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/rp2/RP2.md b/rp2/RP2.md
index 09e7b1f..0188234 100644
--- a/rp2/RP2.md
+++ b/rp2/RP2.md
@@ -85,7 +85,9 @@ is rapid with transmission running in the background. Returns `None`.
 ## 1.4 CS/
 
 The application should assert CS/ (set to 0) prior to transmission and deassert
-it after transmission is complete.
+it after transmission is complete. An external pullup resistor to 3.3V should be
+provided to ensure that the receiving device sees CS/ `False` in the interval
+between power-up and application start-up. A value of a few KΩ is suggested.
 
 # 2. Nonblocking SPI slave