TI-83 Plus
SILVER EDITION
TI-83 Plus Developer Guide
6
Beta Version May 16, 2001
If the ‘nz’ bit is set, the DBUS hardware assist has stored a byte for retrieval OR IS IN
THE PROCESS OF RECEIVING A BYTE AT THE PRESENT TIME. This is the only
reliable way of determining activity on the DBUS on the TI-83 Plus
SILVER EDITION
hardware.
Sending DBUS Data/Error States by Toggling the
DBUS Lines
Frequently Apps will attempt to flag an error to the DBUS by taking both DBUS lines low.
Similarly, Apps may attempt to toggle the DBUS lines from within the App rather than by
invoking the RecAByte and SendAByte routines. These actions will cause the DBUS
hardware assist to reset each time either (or both) of the DBUS lines are placed into the
low state. If the DBUS assist hardware is in the middle of a transmission when the App
toggles the DBUS line, the transaction is aborted and the byte being sent or received is
lost.
Unexpected Error Conditions
If the DBUS hardware assist unit is sending data to a DBUS device and that device
asserts both DBUS lines low, the DBUS assist will abort the send with an error condition.
The indicated error will be TIMEOUT, as the hardware will only know that it could not
send the byte in the 2 seconds allotted.
Summary
In general, it is always safe to call RecAByte and SendAByte. Direct access to the
DBUS lines is discouraged as it may cause communication problems.
To Next Page
Loading...
