diff options
Diffstat (limited to 'protocol')
| -rw-r--r-- | protocol/ibm4704.c | 40 |
1 files changed, 33 insertions, 7 deletions
diff --git a/protocol/ibm4704.c b/protocol/ibm4704.c index d3fbcc541..10e229fd1 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) { |