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authortmk <nobody@nowhere>2014-02-10 11:05:18 +0900
committertmk <nobody@nowhere>2014-02-10 11:05:18 +0900
commit902afcc509cf5d84b24f71297591cb7cb3d7493d (patch)
tree9e18b65bf2ce218cd7cf722d210ef0257892746a /protocol/ibm4704.c
parent0f827cf94ccd6bef490ba889bc86c61483b1eb80 (diff)
Add doc 4704.txt and protocol comment
Diffstat (limited to 'protocol/ibm4704.c')
-rw-r--r--protocol/ibm4704.c40
1 files changed, 33 insertions, 7 deletions
diff --git a/protocol/ibm4704.c b/protocol/ibm4704.c
index d3fbcc541d..10e229fd15 100644
--- a/protocol/ibm4704.c
+++ b/protocol/ibm4704.c
@@ -23,6 +23,25 @@ void ibm4704_init(void)
inhibit();
}
+/*
+Host to Keyboard
+----------------
+Data bits are LSB first and Parity is odd. Clock has around 60us high and 30us low part.
+
+ ____ __ __ __ __ __ __ __ __ __ ________
+Clock \______/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/
+ ^ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ___
+Data ____|__/ X____X____X____X____X____X____X____X____X____X \___
+ | Start 0 1 2 3 4 5 6 7 P Stop
+ Request by host
+
+Start bit: can be long as 300-350us.
+Request: Host pulls Clock line down to request to send a command.
+Timing: After Request keyboard pull up Data and down Clock line to low for start bit.
+ After request host release Clock line once Data line becomes hi.
+ Host writes a bit while Clock is hi and Keyboard reads while low.
+Stop bit: Host releases or pulls up Data line to hi after 9th clock and waits for keyboard pull down the line to lo.
+*/
uint8_t ibm4704_send(uint8_t data)
{
bool parity = true; // odd parity
@@ -85,13 +104,20 @@ uint8_t ibm4704_recv_response(void)
}
/*
-Keyboard to Host:
-Clock ~~~~___~~_~~_~~_~~_~~_~~_~~_~~_~~_~~~~~~~~ H:60us/L:30us
-
-Data ____~~X==X==X==X==X==X==X==X==X==X________
- | 0 1 2 3 4 5 6 7 P(odd)
- | LSB MSB
- Start bit(80us)
+Keyboard to Host
+----------------
+Data bits are LSB first and Parity is odd. Clock has around 60us high and 30us low part.
+
+ ____ __ __ __ __ __ __ __ __ __ ________
+Clock \____/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/
+ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____
+Data ____/ X____X____X____X____X____X____X____X____X____X________
+ Start 0 1 2 3 4 5 6 7 P Stop
+
+Start bit: can be long as 300-350us.
+Inhibit: Pull Data line down to inhibit keyboard to send.
+Timing: Host reads bit while Clock is hi.
+Stop bit: Keyboard pulls down Data line to lo after 9th clock.
*/
uint8_t ibm4704_recv(void)
{